While a solid casting will accomodate a custom bolt spacing and allow it to be placed on a block other than the typical Chevy 153 and 181 blocks, provided it doesn't interfere with any casting features of the head like rocker bosses or valve cover rail, etc... I don't think you will be able to gain any amount of water passages to create a water flow channel, at least not from any of the solid billet heads I have seen as a comparison.
