Although you can make an RB engine as light as a stock LA engine, I'd stroke a small block. I met a guy a couple weekends back at the Goodguys Northwest Nationals with a beautiful 66 Satellite vert. Stroked 360. I believe he had 3.91 gears. The car goes 0-60 in under 4 seconds. For street driving you'd get great handling and acceleration like a scalded ape.