Chamber size on my heads is 64cc, kind of large without the right piston. I can lose a few cc's by milling. World's tech sheet says 7 thou per cc, max cut of .040.
With those numbers the best I could get the head to would be 59cc but I don't think I would want to cut all at once.
I did see that JE Piston offers a 13:1 with a 62cc chamber in their SRP line for $500 & change. Don't know that much about JE or the SRP line but it is a consideration and fits in line with my 'bucks-down' mentality.
Murff