Well, someone has to be the lone voice in the wilderness calling out for a frame swap. The problems that people tell you about are brought on by their lack of knowledge of how to do it cleanly and effectively.
First of all, you need a flat, level working area. The garage floor is not level. What I have done in the past is to shim up the difference with 3" x 3" or 4" x 4" pieces of thin wood glued together. I started at the highest point of the garage with no shims and shimmed taller and taller as I went downhill. These stacks of wood shims were placed about 6" apart and glued to the garage floor. When I had an area large enough to work off of, I laid 1" particle board down over the shim stacks. Three boards were used to make the working pad 7 ft. x 12 ft. Each board was 7 x 4 because I cut off a foot from the end of each of the boards. When I was through, I had a working pad that was within 1/16" of being flat and level from one corner to the other. At the low end of the garage, the shim stacks were 2 3/4" tall. This is not a costly operation. You need a 48" level, a couple of door skins, some 1 x 2 or 1 x 3 material, some 2 x 4's, some wood glue and three 1" pieces of particle board. Less than a hundred dollars can build a pretty nice flat board.
Going from one stack to the next stack, lay the end of your level on the last stack you glued down. Under the other end of your level, build your stack to come up to the underside of the level. Now, build all the stacks in between to come up to the underside of the level. I'm probably making this sound more difficult than it is.
In my opinion, the way to do it is to remove the cab from the original frame, clean everything up and install new frame biscuits between the cab and frame. Move the truck onto the building pad. Make sure the front wheels are sitting straight ahead. Measure the front track and the rear track and write down the measurements. This is the measurement from the middle of the tire on one side of the truck to the middle of the tire on the other side of the truck. Once you have the front and rear tracks written down, remove the wheels and tires. Drop the body to the ride height that you want when finished and insert jackstands under the frame at each corner of the cab. This is where you decide what the finished product will look like, whether you want it at stock ride height or dropped a little in the front or dropped a little in the rear or dropped a little front and rear but sitting level or whatever. Drop a plumb bob line from the center of each front spindle to the pad surface and make a mark (that's what's nice about having a particle board surface to work from, you just make your marks with a carpenter's pencil). Now go to the rear and drop a line from the center of the rear axle and make your marks on the pad. Use your tape measure to measure corner to corner each way diagonally to make sure you have a rectangle. If not, move your front marks to make it a rectangle, not a rhomboid. This is where we will correct any tweaking that has been done to the frame in the past. We will have "square" frame marks on the pad to construct the new front and rear clips when the project is done so the truck does not "dogleg" down the road. Draw a line between the rear X's. Draw a line between the front X's. Draw a line between the front and rear X's on each side. Measure again to make sure you have a rectangle. All further measurements will be taken from this box you have drawn on the pad.
Make up a sturdy fixture from 1" square tubing that will bolt to fender mounting holes in the cab and will locate the hood latch. You'll want to bolt this locating fixture back onto the truck when you are trying to locate the hood latch on the new front clip core support.
Cut off the front clip of the old frame, leaving about a foot of material in front of the firewall. Same at the rear, cut off the frame leaving about a foot behind the cab.
Now, you have to determine what donor you're going to use. You're going to use the front and rear clips from something. The Chevy Blazer will be too wide. You want to use a donor that has a front and rear track that is close to the Dodge to keep the project from looking like some hillbilly did it. While it is true that you can use different wheels with different backset to move the tires in or out, I consider it a cleaner job to get it right with the stock donor parts, then you don't have to spend money for different wheels.
You have the measurements of the front and rear track on your truck. Use those measurements to find a suitable donor car or truck. The wheelbase of the donor will not matter. We're going to use only the front and rear clips out of the donor. Ford Junkie was thinkin' Chrysler. Take a look at the Dodge Dakota pickup. The Gen I Dakota (narrower track than the Gen II truck) was made from '87 to '96 and the '91 to '96 used a 318 V8 as an option, so everything would be set up for the "A" motor of your choice, 273, 318, 340 or 360. There will be no need to fabricate motor mounts or moving the motor to the passenger side to miss the steering or any of the other contortions usually associated with a frame/clip swap that isn't well thought out beforehand. Of course, once you have your hands on a 360, a 408 stroker kit is only a phone call away.
Now, here is where most guys mess up on a clip swap. They fail to secure the suspension at ride height before welding the clip to the center frame portion. In other words, with weight on the suspension, the control arms are at a certain angle compared to the ground. For instance, if you get up under a Dakota that is complete and running around on the street and put an angle finder on the bottom control arm, you might find that it is level with the ground. But once you cut the clip off the front of the Dakota, there is no weight on the torsion bar and the lower control arm is no longer level with the ground. So, what you want to do is lay an angle finder on the lower control arm of a running, driving example of the donor you will use. You will also want to record the angle of another part of the front clip on the actual frame member front to rear, so that you can repeat that angle when welding your donor clip onto the recipient frame that lays under the cab. If you don't get the front to rear angle of the donor frame correct, the angle of the motor will not be correct. Record those angles. You will use it to set up your front clip by making a fixture to hold the suspension at the angle you recorded. When you do it this way, the front suspension is at ride height when you get done. You will put the centerline of the front spindle at the height off the pad that you want for whatever tire you want to use, for instance 14 inches for a 28 inch tire.
You will check for square by dropping a line from tip of the donor spindle to the pad. You may have to extend lines on the rectangle you drew on the pad. That's ok, that's what the rectangle is for, to have a base from which to extend lines to work from.
Here's a tutorial I wrote for the wiki concerning a Dakota swap into a '49 International.
The other choice I would look into would be a G body GM car, '78-'86 Monte Carlo, El Camino, Grand Prix, Cutlass.