John , I agree with Todd . the 16 hp SA class is pretty popular in most areas. 12 hp SA's are around in some areas. you may want to check the rules with the club you plan to pull with to see what they have for class's. other things to consider . most all of the strong runners need steel cranks,cams and timing gears. if you get it to turn hard the stock cams break , the teeth come off the stock cam gear & the cranks have a nasty habit of becoming 2 piece. as for rod & pistons . all of the parts manufactuers (vogol's,lacota, super cub) have a rod & piston package available for the 30 OS SA motors. My brother Jim has dyno tuned a couple 16 hp NQS SA engines now and it looks like you need 40 or better.