if your lookin for advice, tell more of the build,especially what are the operating rpms gonna be then youll get advice from strangers that may or may not know what would suit your needs...off hand im guessing a 310 to 325 cc head would work well depending on rpm...good luck and i hope your vehicle can handle all the power your gunna make, ill take a guess and say peak hp will be around 7000 or so rpm so id lean twards the 320cc head if it was me and without seeing more info
happy motoring 8)