Most of the responses here say save the money and go aftermarket heads. I agree to a point. You can run what you have and ring the most out of them with a tunnelram and big roller, and if you do it right with a very efficient oilpan to reduce windage, and very well designed piston and ring package I think its possible at a sealevel track. It will be on the edge though!
I would set the shortblock up with a zero deck to allow the move to either Indy SR or 440-1 heads to pick up the pace at a later date and replace those crack prone 906s.