Greetings, me, welcome to The 'Bolt.
As for your question, a simple one word answer-
DON'T!! 
Let me elaborate-to my thinking, unless you're one darn fantastic metal fabricator, doing this kind of swap will result in endless frustration and possibly a scrapped truck cause you got in over your head.
If you're serious about a frame swap, think about something with a similar shape, like maybe a Chevy S-10/GMC S-15. The car chassis (Buick Regal midsize) is a
perimeter style frame, where the framerails are wider between the front and rear axles (the middle of the frame is almost as wide as the axle track width. There's also one huge kickup over the rear axle and suspension area, so you might have to kiss part of your box goodbye for clearance. Frame horn hookups for the bumper mounts (particularily at the front) are very difficult due to the location of the steering box. The list goes on...and on...
Have I scared you yet?
Your best bet would be to keep your existing frame and upgrade it with the proven aftermarket stuff (Mustang II IFS, lowered leafs out back, etc). Scrounge e-bay for deals on parts, they can be found. If you just
have to have some part of that Regal under your truck, try doing a subframe clip-check out the "Tech Tips" section here at Stovebolt .com and you'll find an article on this exact swap done by one of the fellas here, complete with pictures!
Not trying to rain on your parade, just give you some idea of problems you might encounter. If you have any other ideas or questions, don't hesitate to post 'em, chances are someone here can give you a hand.
Regards,
Wannabe
