from what i underatand there is a company who has drop in hc pistons for the 865. i believe it was JE but i am not positive. but the 904 is proven with many members on here having great luck with it. by next year i will be able to report how i feel about it

Frank

(Former)05 BA tbike pipes, ai removed, Freak, mikuni hsr 42's, 904, ported/polished head, 1mm oversized valves NOW-2010 silver and black tbird