From gearhead EFI:
The 1995 has a 19167427 PCM IIRC. Commonly referred to as a 7427, best of the OBDI computers since it was the last before OBDII. It's actually a PCM, not an ECM since it controls the transmission on autos. It's no slouch, pretty much as fast and powerful as OBDII stuff. I had one in my 89 TPI truck for a while. Was a great little box. I eventually converted to OBDII with a 411 PCM running sequential TPI but that's another story for another time.....
The 7427 uses a MEMCAL:
You must be registered for see images attach
Seen as a gen 1 MEMCAL in the pic above. The PROM is for the 7477 ECM from the earlier TBI trucks.
You don't need to mess with the wiring/PCM in your case, which is a simple engine replacement. You will want to swap out the MEMCAL eventually (or right away if you have it).
A 350 4l60E is BCC BYJK if I recall. The BCC is the calibration for the particular engine transmission combination. Might want to research that BYJK though, been a while since I messed with OBDI stuff.
Also, I do believe you can swap in the long block under all the 305 systems and it will run acceptably. Same throttle body, injectors, MEMCAL, etc. The PCM will up the fueling in response to teh O2 sensor feedback. The question is whether or not it will all have enough authority to reach Stoich on the 305 stuff. I seem to recal that it does, but you're running at it's upper limits. Again, read up on that becasue it has been several years since I messed with a gasser (moved on to diesels several years ago), let alone and OBDI TBI truck.
If you haven't done engine removal replacements much before and/or are working outside, I would suggest you have alternate means of transportation lined up for your Monday morning. Sometimes it goes smooth as butter, sometimes not-so-much. Especially if you start deviating from straight up stock stuff to things like headers and resulting exhaust changes.
Good luck.
