V2.2 gearbox they call it. Longer and with the trigger mech out front. The cylinder is not larger - in fact I think all the internal parts are the same (except the nozzle may be different?).
Only thing I've done to mine is Sorbo/AOE, longer barrel, unported cylinder and running it off a MERF3.2 on 11.1V. Oh yeah, I completely burned out the contacts on 11.1V before I installed the mosfet.
I find the hop-up is very tight, so most buckings will be too thick to fit. I did get a Modify Baton Ryusoku to fit though, surprisingly.