[Jac Mac]

This pic should give a better idea of lube height/level in the unit, note the level hole is a bit lower than the axle tube diameter so filling until it runs out the axle tubes will be too high, I dont see anything other than removing the diff head assy & fitting a level plug in the axle housing, if it has not got a drain plug you could fit one of those as well, You could drill & tap for a 1/4" npt type taper plug in the axle housing rear cover at the correct height with some grease to capture swarf etc, or better still drill a small 1/4" hole & use a taper punch to 'flare' the hole inward prior to threading for 1/4 npt to gain a couple of threads.