I have to vote with the guys who suggest building your own frame. I have not priced steel tubing lately but you should to build a frame for under 100.00.
You might try this, take some 2x4's (wood) and lay out your frame Used wood is ok, after all it will be a rat rod. Anyhow cut and fit that to decide how things are going to set up. Mistakes are a lot cheaper and you can stand back and look at it and see if the ideas work or won't work.
When you do cut your steel tubing mark out all of the sections on the tubing before cutting so that you can have the least waste of metal. This way you can save a few inches when you cut the angles for the kickups.
As for a front axle an early Ford I beam would probably be the easy way to go but there are a few other methods that don't look all that bad Maas makes some strong but not all that spendy tube front axles ans suspension pieces. Another idea is to build batwings that bolt to a 40's / 50's pickup front axle to turn it into a cross spring axle. I don't have any photos available on a disk at this time to be able to show them but the examples that I have seen were pretty clean.
I'd go with a mopar rear to match the engine. The 8-3/4 is easy to find and plenty strong for most rigs.
Like one of the other guys said, it is easy to build your own body. Swap meet cowls arn't all that expensive or make your own you might even cut down an older pickup cab. like out of the 40's or 50's Just don't pay much of anything for one if you do.