Powerglide / stall converter question

Guys,
I've acquired a car that currently has a BBC 468 and a Powerglide tranny with a 10" 4000 stall. Some are telling me that the 4000 stall won't be very streetable, and I tend to agree after a couple cruises around the block. The car has a tranny cooler, but I still worry abou the heat.

The previous owner removed the 8" 5000 stall and replaced with the 4000, but stated that it was the same converter as a TH350. He also mentioned having to have a new input shaft built for the 10" converter, which is where one of my questions comes in.

1.) If I move to a smaller rpm converter, do you have recommendations
2.) Not being an expert on automatic transmissions (I've always been a Muncie guy, but evidently this car went through three of those before they converted to the PG), the need to create a new shaft is confusing me. Could it be because the 8" converter had different splines/spacing?

Thanks for your help...

Forget about the stall converter recommendation guys. I'm going to verify the cam tonight and take that, along with some other info, to help with that decision.

If anyone can enlighten me about the shaft change, I would be open to why that was needed. I guess I may not know for certain until I pull the current converter and look at the difference.

Thanks again...

Could be they were twisting up the stock shafts and decided to go to something a little more substantial....
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