ORIGINAL: DaveSR71
I comparing the 5103 to a 5224 with out disassembling:
The 51 is smaller than 52
The 51 appears to be bushing crank.
The 52 appears to be twin ball bearings.
The finish on both engines is similar with the in box 51 being slightly Grayer.
The 5224 on the left is the 29-IV Special with twin ball races and a different crankshaft using a 1/4 x 28 prop thread instead of the usual 7 x1mm. The 5103 is a 29-IIIB and yes, a bushed crankshaft.
That's interesting about the Super Typhoon in those instruction sheets because I've never heard or seen that reference before.
Seems like I might have to strip a couple of engines too and do some measuring of the ports like flyingtigre did.