Air Hobbies offers conversion services for installing needle bearings on the ST and Moke connecting rods. If I recall correctly, Ralph Cunningham (rcignition) has performed this on the ST in the past, but does not any more. I believe the reason given, at least for the ST is that the crankshaft metal is too soft to run needle bearings directly on the crank pin. I also have read that some have ground down the crankpin and pressed on a hardened sleeve for the needle bearings to run on. I don't know how successful this approach has been.