I'd pull the whole motor so you can get the accessory setup above all else. 4L80E? If so, I'd pull the whole powertrain and engine harness/PCM. If it's just a 4L60E, I'd pull the trans and sell it separate; maybe still pull the engine harness. There's not really anything else that translates between the GMT400 and the Square. If you're gonna rebuild and swap just that motor, I'd lose those heads. The bottom end of it is definitely worth having since you can roller cam it, and the one piece RMS should last a lot of leak free miles if done properly, but the 87-95 top end sucks in terms of power potential. The TBI system is more workable than people realize, though. If the newer Burb has a 4L80E, and you want to swap the whole drivetrain and harness/PCM, I'd verify that the MEMCAL in that newer ECM can be tuned as easily as the PROM in your square Burb before you upgrade anything. Just letting the cart get ahead of the horse a little, but it's good to brainstorm.