My Keith black block is 4.500 and the mega block I bought was good at .030 (440). I had a 440source kit at .055 over and bought.030 pistons from Brandon because I was going to waste block thickness when the bores were so nice. I had to rebalance everything but ohhhh well. Then I sold it off 4-5 years ago when I was having so much fun with small blocks. The keith black block sits all together doing nothing.