[brainsboy]

A 69 block will have no problem with 500 to 575hp, you can even run this hp with out a main girdle. These blocks are pretty strong, and with a main girdle will have no problem in the 700hp range. I'm currently building a 700-800hp 351 stroker motor, which uses a 69 block. One thing to check is how your block was casted. This can be done by drilling into the casting and checking the thickness at point locations, also looking at where the cam journals were machined will show if it was properly casted. The castings do have differences, but for the most part at only 500hp you will be 100% fine with no problems. If you cant find a 69 block, my next choice would be a 70-71-72. I wouldnt go with 73+. Although the casting stayed the same for 73 and 74 the nickel content actualy dropped making them not as strong. If you have trouble finding a 69 block, I have a few of them in my garage I can sell you.

Ben