Heres wat id do.
Use a fror type mount, can buy base and fab you own, or buy complete for 300 or less, make a square shaft, chop and shorten rear. Get a used adapter off here from someone, whichever brand you prefer, marlins is the best tho, get a top shift case off here, and do your duals for around 500 bucks, and you be crawlin.
Also, you could do a sinlge 4.7, for ai think marlins is 400 bucks, and not mod anything at all really, just inside of case slightly, and have damn near dual ratio. Just wont have seltion of gears, but you can go duals later, and have ultimate case.