70 Jimmy 4x4 driveline upgrade

[k-nuts]

So I’m going to upgrade the drivetrain on my Jimmy. Currently it has a tired leaky 350, a very leaky th350, and leaky 205.
I have opportunity to replace the 350 with a gm crate engine around 400hp. & I’d have the 205 gone through and resealed.

My Main question is the transmission. Rebuild/beef up the th350, replace with new th350 or swap to 700r4 for the overdrive?
(When I swapped the 2 speed for a 200r4 in my 68 firebird it was pretty much just change Xmember and setup tv cable and lockup switch.

Not sure on dimensions or what else is involved in changing to a 700 and if it’s worth it. I looked through posts but a lot are older and apply to 2wd trucks etc, so figured I’d ask again.

This is not a daily driver but an every so often weekend cruise around vehicle. Of course the more I do to it, the more I want to drive it. I just started really messing with it again this past year or 2 after mostly sitting in the garage for over 12 years. I put a hydro boost brake system, brakes, 33” tires, soft top and dash stuff so far. I have 2.5” springs, shocks, and stabilizers waiting to go on so some progress is in the future.