[bwood]

The 4.3L V6 utilizes the same bellhousing pattern and dimensions as the V8 engines. The converter will have a higher stall rpm than a converter designed for a V8. Converters are selected to allow the specific engine it is bolted to, to get into the appropriate rpm for that engines power curve. A converter from a V6 will work on a V8 but not the other way around. You will see the engine rpms climb a little higher before it kicks all the way in. More than likely, it will only be a few hundred rpm. You probably already know this, but do not try and use your converter from the bad transmission in the "new" one. Either use the one that comes with it or buy a new one.

As for the flexplate, they should be the same. The mounting flange on the end of the 4.3 and the one piece rear main seal SBC engines is the same. They also use the same converter so the three converter holes are the same. A quick look on Oreilly Auto's website shows the same part # for both vehicles:

Pioneer #FRA159 or FRA159A for the heavy duty.