Been there, Done that.. .Going through this very same issue right now..mine is a 4.35 bore, 4.375 stroke, 520" stock block 440, 12.4 compression ratio, indy -1 heads from Modern. 3200 lb car runs 9.80 at 138 mph, dynoed at 760hp The block was hard blocked and girdled, aluminum Main Caps. had a thrust bearing issue, pulled it apart, and the block is BROKEN!. where it is broke, the hard block and girdle did not help. I am going to build another one, this time I will NOT waste my money on the hard block and girdle. I talked to Cab Burge about this issue, and you might PM him, and get some good info first hand. As stated above, be very conservative on your tune, Detonation is the big killer, and the other helpful advice I recieved is to lower the compression to around 11 or 11.5 to 1. keep us posted, I am very interested in what you finally decide to do, and how it turned out for you.