was in the market for heads, going to try 5.3 heads, found some locally for cheap price(stock w/ 1200mi.). they are 862 castings and was going to get them machined. my question is what are the diff. between the castings, chambers ect. and what is the most efficeint chamber size (59cc, 62cc,64cc). mods in sig , plan on spray sometime this spring (75shot) max , I run an indexed class. thanks for any help