Back in my hotrodding days 50-something years ago, our slogan was "There's no substitute for cubic inches!" With off-frame resto-mods, it's more like "There's no substitute for cubic dollars!" Anytime the frame and the sheet metal get separated, the dollar-gobbling gremlins start multiplying geometrically, and there's always someone lurking in the shadows who claim they can solve all the problems by selling you something- - - -a trick suspension system, fancy wheels, a disc brake conversion, air bags, etc. These people are not necessarily your friends! About a year ago I did a pre-purchase inspection on a 54 Chevy 3100 that had gotten the full resto-mod treatment. An overseas buyer commissioned me to do a photo shoot and a test drive and file a report. The asking price was $70K, and the seller claimed he was barely breaking even. The steering system was just short of being deadly dangerous, the result of a poor routing job of the steering shaft and universal joints which made the steering try to lock up every 1/2 turn of the steering wheel. There were a few other pretty serious mistakes made during the project. I really doubt if the buyer took the bait, or if he did, I'll wager the price got heavily discounted to accommodate the repairs I recommended.
As several others have suggested, do your homework before you pick up a wrench! Have fun!
Jerry