Yes the main shaft had a thrust bearing between the top tail drive gear (above the main gear) and the bottom of the upper shaft support bearing block and was a mistake in use. It basically applies pressure against the inner race of the radial bearing above it and sat on the aluminum tail drive gear on the bottom which is locked to the shaft by the pin anyway, so it is in essence pointless as it never sees any actual use other than a spacer.
The frame stiffeners that came with the HD model were an upgrade that many felt was necessary due to the lateral flexing of the frame under hard flying. This flexing many felt resulted in the smaller clutches breaking and bearings wearing out and falling apart in the pinion bearing block as well as the vertical supports breaking or the CF fan plate that was mounted to it eventually breaking and or the lower frame breaking at the point just ahead of the fuel tank. The frame stiffeners apparently reduced that for alot of G20 owners that flew 3D and or had higher HP modded engines that put more stress on the already feather light frame.
So if you fly 3D the stiffeners are a good thing to have based on what they actually accomplish.... the thrust bearing was pointless when a collar with a set screw was all it needs there.
showing a preference will only get you into trouble, 90% of everything is crap...