ORIGINAL: HerrSavage
The only difference between the versions is that the 30X is a truggy version - i.e. with closed backplate. Which obviously isn't in a Savage... The Spec 3 28 also had two versions.. The Losi XXL basically has a Spec 3 pullstart, the new 8T 2.0 the same engine but with closed backplate - i.e. the LRP Spec 3 "Truggy" version.. They're now called Losi 454's though - and are orange...
the LRP zx .30x competition has a different sleeve as well, 7 port vs 5 IIRC
and is rated at slightly higher RPM and power with rev's at 33,500 and power at 4.21
i'm not 100% shure but i think that the backplate/rotostart from the .28's will work on the .30's