You won't know what transmission to use until you have your axle ratio - cheaper to choose OD Y/N than installing new R&P.
Your stall speed will depend on your cam.
If you have the room, an Atlas 4200 is a much better (but $$) choice.
You can buy an entire Toyota L6 twin turbo engine & automatic transmission, used, for about $3,000 but you'll need aftermarket electronics to control it.
There is no "going rate", a 12 port head alone is over $3,000 without porting, springs or rocker arms.
