I am familiar with your questions....had two of them actually, and got familiarized with them quickly.
There basically 2 different G2160's.
One was a G2160.
The other was a G2160-48RS.
The "48RS" version is a rear discharge direct-shoot bagging system. The regular G2160 had a side discharge deck.
Big difference too....the 48" rear discharge DECK cannot be converted to a side discharge; or at least not without completely redesigning the entire deck system, and I mean completely redesigning it! That is a complicated deck and bagging system. HOWEVER...there was a rear mounted side discharge adapter for them, that is no longer produced. I can't even remember the wholegoods number. Basically you'd remove the rear bagging attachment and attach the side discharge baffle. The downside is that if the chute assembly under the tractor was rusted (like most of them were/are), the rear discharge did not work all that great. Pretty poor actually. The side discharge baffle assembly could be made pretty easily with some sheet metal, IMO, if you're good with a blue-tipped wrench, hammer, and welder.
The other G2160 was a "regular" side discharge, I think 48", 54" and 50" were option on those. I liked that mower. They cut really good. I hate the tractor though...at least the electric power steering. I never could keep one going in a straight line when the EPS worked and when it didn't work (often), it was worse than having manual steering, sorta like driving a car with power steering and the power assist not assisting-and this was worse on the G2160 because of it's high travel speed. Mine mowed at 12.5 mph. It was honestly dangerously fast but the neighbors got a kick of watching me cut the one side of the house because I could do it in no time flat (all 100% flat, smooth ground).
If they'd have only put the G2160 transmission in a GR2100 with the regular GR cutting deck, it would have been a total winner, IMO.