I put the Saginaw box on a '66 I used to have. It was actually pretty easy and didn't cost too much. You can get the box cheap to free from someone who went to power steering. Advance Adapter had all of the steel pre-cut to convert it; that was the only real cost.
'81 Scrambler w/ FI 360 AMC, 33x12.50 BFG M/T's, 5" of lift, ARB'd Dana 44's F & R, Dana 300 clocked & twin sticked w/4:1, Warn XD9000i, etc...
2002 Grand Cherokee Limited, 2008 Overland Grand Cherokee, a 1976 CJ-7 in pieces and 3 more off-brand 4x4s...............