Yes it works out good. I have a 360 with the KB107 pistons and X heads (same chambers as your J heads) that have been shaved .020 and they cc'd out to 67 cc. The pistons are .020 in the hole and the compression figures out to be 9.8 to 1
I do have to run premium in it but it's fine on pump premium. If your heads aren't milled any the comp would be real close to 9.5 to 1