Building a frame would be expensive. Check with Fatman Fabrications. This is mega dollar street rod stuff.

If your frame is rusted beyond repair, the only easy swap is another frame from the same configuration and year of your truck. You may be able to repair your frame, or alter the wheelbase of a similar year frame with a different wheelbase, but this demands proper skills and procedure and you may compromise safety.

Fitting a frame from an entirely different vehicle would be a nightmare.

Since we don't know the extent of damage you are dealing with and you state your goal as a smooth ride, have you considered a Crown Vic IFS swap? Some of the 72 and earlier crowd have done this with success.

 

I hate to generalize here but sometimes the old adage is true: "If you have to ask, you wouldn't understand".

While I admire your passion for your truck, I don't believe you'll ever finish a project like this unless you've done some serious fabrication and/or swapping in the past.

What is your prior experience with mods of this (or close to this) scale?

 

Umm... a car frame/suspension under a truck is easy...

Just buy a Chevy

 

Yeah, my buddies full size 4x4 chevy got stuck in 3" mud and I had to pull him out with my ranger

 

I can see where your coming from. I've never found something I couldn't do though. Got a free motorcycle at 15, built a cafe racer and taught myself to weld. Bought a 78 bronco at 17, put on heads and an intake. All without any prior instruction. Not trying to toot my own horn, I just haven't found my limits yet.

 

Lots of cars today don't even have frames. The ones that do are perimeter frames. The truck is a ladder frame. Your best bet is to modify what you have.

On the easy side, when was the last time shocks were replaced? Radius arm and pivot bushings? It wouldn't be the first time someone has complained how crappy the ride was and everything is whipped.

If you really want a car ride it is possible to swap a crown vic front suspension in. The frame is just a touch too wide so it will need some notching and boxing but it's doable. For the rear you can get some light duty springs or even remove a leaf from your pack, flip the axle and C the frame.

Another option is to use drop beams in the front and flip the rear. Get some MOOG 818 or 820 springs or custom and follow the above for the rear.

If you want to go totally car I've seen people put the 01-04 cobra IFS in.

The car suspension isn't going to be cheap. Drop beams will be less and simple maintenance will be the lowest.

 

Agree with everyone else - modify what you have (or get another truck frame and modify that). Suspension on any frame is going to have roll centers and suspension geometry designed and calculated for the weight distribution and center of gravity for whatever vehicle the frame belongs to. Even if you did all of the fabrication necessary to put say, a crown vic frame under the truck, chances are it would still ride like dog crap and be unpredictable and possibly dangerous as well.
There's a lot you can do for ride quality by messing with spring rate, dampers, anti-roll bars, and tires.

You could make your own frame, but there'd be a lot of engineering learning you'd need to do. And I would definitely destructively test welds you've made before taking something on as improtant as your vehicle's frame. It's great that you taught yourself how to weld, but that also means you have no outside reference for how skilled you are.