Now a dose of reality... With 906 heads to run 10.5 C/R you'll likely be mixing race fuel to keep from detonating... Open chamber iron heads are not your friend.... But since you have fresh 906's I wouldn't be changing them... But I would consider having them milled.. Take the heads off & get us a number... If the pistons measure .090 in the hole & you cut the heads .050 & use a thin gasket you'll be around 9.5 which with open chambered iron heads is right where you want to be... Get a depth & get back to us..