if you want a happy high revving ka that would last longer than stock specs then im thinking a set of custom 11:1 "short" pistons with a longer rod, effectively changing the stroke ratio a little. carillo rods... mmmmmm... from the looks of stock pistons you MIGHT be able to get rod thats 5mm longer but then you have to take into consideration of rod to block interferance. well thats what i have been looking into lately. if you have something that you want to be rev happy then you might want to go the route of a dry sump oil system. but now we are talking serious money. nothing that i know of is interchange able between the single cam and twim cam heads. i do believe the valve spring seats are the same. i think i used some single cam ones in my twin cam. cant remember though.

but if you do touch the bottom end then youll need to get it balanced, which is even more money.