I've always heard good things about the Kawasaki, Honda, Vanguard etc. But I would NOT buy anything from BU. It either won't work or you may never get it. I would get it from Tom at
http://www.cartpartsplus.com/ 
Also, I'm not sure if Ron sells big blocks or not, but if you're looking for anything else for the cart you can look here also.
http://www.eastcoastcustomcartsinc.com/