there are some nice examples on here, mate, for you to check out. go to the rolla club rides and search thru them for some nice ideas.
i personally am thinking a rotary, like Shane's secksee beast here:
http://www.rollaclub.com/board/topic/12785-13b-turboed-ke30/page__hl__%2Boke+%2B030
so much room and less weight, imho. doesnt have to be a race tuned engine to fly, either.
there are soooo many nice 4 cyl builds to excite you, and me, in the rides' thread.
hope this gives ya something to look into