You will be fine..
Something to think about,,
Make sure you calculate the amount of mateial needed to reduce the chamber 14cc to get your compression of 9.5. The intake side of the head will also need cut, you will probably need another set of pushrods because of the shaft mount rockers. You will probably need to work the intake holes also. When you add all this up it may be a better deal to get the correct pistons.
If it's a fresh engine i would buy the pistons before i choped the heads/intake JMO.