why are you going this route?? just curious

Quite a few of the whitewater boats run SB and they all haul ass.  Being you have a good base of parts for a SB, I most likely would go that route if I were in your shoes.  The two hundred pound weight savings will be big on a daily basis, but as far as gas mileage, not too sure.  You will have to rev the engine higher to make the power that the BB will do just off idle.  Rule of thumb if you run a BB with an A, you will need a B with the SB, to get the same performance.  SB's love rpm.  I am not saying that a SB can't make the same power, but I am saying the SB will have to turn a higher rpm to do so.

no its at the machine shop I will try it as soon an I get it back. Thanks for the suggestion.

I  wonder what impeller the SB likes

From what I've read     the small block makes it's power in a higher RPM than the big block, therefore you go with a B or C impeller.   

My small block will be around 500 ponies I have an A impeller do I need to change for the RPM difference?? Thats gunna suck

My motor is a 383 stroke callies crank,rods,JE pistons,undecided on which aluminum heads and a 100 shot in nitrous. Edelbrock performer RPM air gap intake, gotta figure out which carb I am gonna need. My pump is the new JI with A impeller with droop and diverter. HMMM what should I do??