The 906 heads have the big exhaust valves. That's a plus. If the pistons are flat tops with or without valve reliefs, I would just go with the cam you want and the cast crank is no problem for your purposes. If the pistons are dished out, I would consider replacing the pistons and internal balancing. For the cost and time it would take to redo the motor, you can easily handle the externally balanced issue if the pistons in it give you any compression over 9:1...unless you are trying to build an all out race car?
