Well, I'd go with a replacement 4.3 engine, but the reality part is that the 350 is the cheapest engine to rebuild, and believe it or not, the v-8 engine actually runs smoother, there was an odd vibration issue with the 90 degree v-6 design even though it was a 350 with 2 cylinders missing.
So I am gonna look for a stock 350 out of a '92 pickup with the AOD, and get the computer, and engine complete from throttle body to oil pan, and see what happens... Now all I need is some money....
As far as clearence... It will clear, but I have to run an electric fan behind the grill, and eliminate the fan bolted to the water pump....