What he said ^^^^
The T67a originally had an O-235 (115hp) engine that was upgraded to an O-320 (160hp) in the T67b. The T-3a and the T67M260 had an IO-540 (260hp) engine. Why the T-3a had the same smaller rudder fitted to it that the earlier smaller-engine birds had, I have no idea - but I do know that if I was spinning and aerobating in the US where it is often 'hot and high' I would want all the rudder I could get in the breeze!!!
LJ