Gear Spread on a 700R4 is 4.37:1
Gear spead on a Th350 is 2.52:1
Both can be built plenty strong. I would take a 700R4 over a TH350 in most circumstances, much better gearing for wheeling, epsecially if you are hogtieing yourself with a 4:1 T-case.
But if you are going with a Dana 300 case then the 700R4 is going to give you fits trying to route a front driveshaft.
Of course, a Dana 300's going to need some help behind a 383...