Look at the first 2 digits of your model number. If it is 28 you are O.K. If it is 31............well no. That is the USLMRA, not shure about ARMA.
FX is limited to 465 cc. That is the 28cid engine, the 31cid is to big. But I'm shure some are running it. and they are probably loosing to guys running the 28!
Later
Paul