I was just BSing with one of these guys backchannel about the early 3 speed t case. A lot of guys run these behind 350s. They do break though, mostly on the trails, the t cases are a little brittle. If you do run one, make sure its (I think) 1970 or later as '69 & earlier are super brittle. It is the case not the gears. The the "t case saver" that some guys sell on mud helps a lot too...
HEre is what I wrote & think about it, if it helps..
The 4 speed case should probably be OK.. They do break though, mostly off road.. My only beef with them is honestly noise, they have a nasty little gear whine to them as the gear cut on them is old school. IF oyu are going to get a NV4500, you can choose to adapter to whatever case you want for the same price. Only additional cost is the actual case. Shop around, you can find a FJ60 era split cases pretty cheap. That is what I would do and run a FJ60 rear axle, slightly wider, and has the e brake on the rear axle, then you are nicely set up.. Hope it helps! Andre