You have two possibilities:
1) Isuzu Engineers left inside the gearbox a lot of space for oil :)
2) Isuzu Engineers put bigger gears inside the gearbox :p
I found a guy who wish to trow away another beautiful engine from the pre-Euro era, it's an iVECO 8060.05 6 cylinder not turbocharger, 5861 c.c., 139 hp at 3000 rpm, max torque 388 nm at 1600 rpm, 5 speed iveco gearbox is included....:cool:

