Best thing to do is buy a head off eBay and have it shipped to KOR to be re-chambered. I have seen 2 heads on eBay in the pass that are re-chambered. You may get lucky.
Just milled is no good. Detonation city! I've done it.
You need a rechambered head, and the shape and dimensions are important.
It will be the best HP gain per dollar you can make on a Blaster.