In either case, (sitting the truck on a new frame OR sitting the frame on new running gear) is going to take a significant amount of fabrication so you must be honest about your fabrication skill AND the depth of your pocket book. Most of these conversions are abortions at best, worthless junk usually. Assuming you give a damn about the look of the vehicle (so you wont have to drive it with a paper sack over your head), the best route is keeping the frame that matches the body and mate the suspension to that. Realize that a 41 Ford didn't get designed with room for a transfer case nor clearance for a front differential, some compromises will be necessary.

Regarding the front differential, the front crossmember hitting is a worry OR the differential hitting the engine is another worry. I have a rock crawler with 40" Goodyear tires and 15" travel shocks and I can still hit the axle snubbers on a large drop. However, the differential solution is fixable. Regarding the transfer case, most people doing the sway go cheap and use some chain drive case. These things are usually huge and take up a lot of room under the floor, requiring the installation of a lump in the floorboard. This, in turn causes other stuff to be relocated.....crossmember, potentially seat frame, etc. The shifter can be a problem if a manual tranny is used. Most go with a 700R4 auto because of the low first gear. The best setup you can probably have for a street truck is a 700R4 with an Atlas transfer case. This pair shouldn't set you back more than $5000. IF you do this right and don't go el cheapo (equates to el crapo), this could be a neat setup. ..... kinda like a period style 4wd.