I just had to make the same decision myself for my 1969 C20 Panel Truck! What I decided on and bought is the NV4500, a 5 speed OD box that has a reputation for being tough as nails among the 4X4 set. They aren't cheap and they require a special gear oil at $28 a quart but the .73 OD makes it all worth while for me. You'll still have the bull gear first when you want it, 2-4 for around town, and OD for the open road. NV4500s are found in mid '80s to mid'90s Dodges and late '80s to early'00s Chevys in 2 wheel drive and 4 wheel drive models. The Chevy 4X4 version is probably the most common and should be a bolt-in for you. Yes, the 205 T-case will bolt right up.
best wishes,
Les
