PICTURES when you start
I cant possibly see why but can give you some ideas.
As stated you will need flipped axles if you just want to spin the engine around. definately put a firewall between all passangers and the engine. I would box the frame in the back where you plan to make motor mounts. Expect to add weight to the front, its going to handle like crap with all the weight in the rear. Plan on all new springs, front and rear, the spring rates will be all wrong. The problem of it always being in front wheel drive when in 2 can be overcome by leaving it in 4 all the time and only leaving the rear driveshaft on. Not sure how the tcase will like this but it sure beats just leaving hubs open. If you are actualy going to do this (nothing personal but it honestly sounds like a 16 year old that wants to dream something different and it will never happen) then you will need good fabrication experience and skill, along with a great understanding of drivelines and such. More experience than the average person who would ask these questions would have