Hi Dana. I have done many swaps, but never into a '51 Stude, do I don't have the exact experience you may be looking for. Has someone specified that the frame MUST be boxed or is this just something that you feel should be done. I don't think I would go to the trouble if this is to be a street truck with a warmed-over 327. If you do feel the need to do it, I would use material that is close to the thickness of the original frame rails (probably something like 0.134") and cut my pieces to the same height as the frame rail with no overlap. I might even recess the plate back into the frame rail by 1/2 or 3/4 of an inch to be able to run fuel or brake lines in the shallow recess. Some of the aftermarket frame makers do this and it looks like it was planned ahead instead of having to hang lines on the outer face of the rail where they can get snagged. I would plate from the frontmost body mount to a few inches past the motor mounts, but again, I don't think it will be necessary at all unless you plan to really beat on the truck. Don't worry too much about how much weld you put on the motor mounts either. I've seen some mounts that look like they would blow away in the first strong wind, but have held up to 3,500 stall, 11 second passes.
Secure all lines to the frame rail with insulated Adel clamps about every 12". I would resist the temptation to run the lines inside the boxed section of the rail because they will chafe and wear holes in the lines from vibration. I have found some very nice Adel clamps at my local Ace Hardware, although they can be found at other sources also. Use the ones with black rubber insulation formed onto them. Counsel with the man at the hardware as to the size of hole to drill in the frame rail for the sheet metal screw size used to mount the clamps.
If you do box the rails, don't make one continuous bead down the entire length at one time. Run a short bead (maybe 2"), then go to another location and run a short bead to prevent heat build-up which could warp the rail. Alternate back and forth until you've welded up the whole length.
One last thing. Jack the truck up and level it at the sills (bottom of the door on the body). Welding anything with the truck sitting on the tires will result in a less than satisfactory job.
Last edited by techinspector1; 01-10-2007 at 08:58 PM.