1984 k30 manual to auto swap question

[DQ81]

Hi.

I've got a 1984 Chevy CUCV (K30) that was converted from a 6.2 diesel to 350tbi out of an '87 truck or van.

It's got the stickshift with L,1,2,3 and I believe the NP205 transfer case (it has the 2wd option) I'm fairly certain it's a factory stickshift truck (trans tunnel inspection panel, stock pedal cluster etc. etc.)

My clutch is toast and the 350 doesn't like the gearing the stick has and I'd prefer an auto anyway. I wanna put a TH400 in there.

Anyone know what gearbox I've got in there now or what would have been stock or where to find the numbers?

Will a TH400 bolt right up and fit length wise to the TC?

Obviously I'll need a flexplate but I should be able to use the existing flywheel right?

I'm hoping I can just swap em out and do the obvious: floorshifter, external transcooler and be done. Not have to mess with reposition the TC or mess with driveshaft lengths...

tia