Take a look at the original TM gearbox:
Hmm, gearbox shell is different. Will ambi selector levers still work with AF shell? As it turns out, the gearbox itself has nothing to do with this – HK416 ambi selectors run by gear set that operates between inside of lower receiver (right & left) and a gear that traverses the gearbox, held in place & allowed to turn by pistol grip.
Note a few minor aesthetic differences… though nothing functionally different. Well, except shell is slightly wider at front – causes incompatibility with some magazines. Big enough issue that I am shelfing the AF shell for now.
TM gears replaced at this stage already (metal bushings too). See photo below – worn stock gear set.