b44.3 diffs in b44.1
 

do they fit?

Yeah you will need to cut the lug off the lower casing

should do- im assuming that the gearbox casing is the same from the 44.1 to the 3 - though you may need to remove the little nodule to prevent you putting the gear diff in the wrong way around depending on your battery configuration.

and youll also need to get an input shaft and input pinion gear for the associated gear diff.