Checking diff condition

Lads,
Front diff went bang at the weekend I have a couple of spares someone gave me but not sure of their condition, they look ok but how can I tell if they are mechanically good - are there some simple checks I can do? Did a search on this but not really any obvious pointers.

Its a 1985 110 diesel CSW.

Check the play between input and crown gear,hold crown still and turn input back and fore. Less movement is best.

Don't forget to give the input a good few turns to get at least one full rotation of the Crown wheel done, that way you will know if there is anything stuck between the teeth of the Crown wheel

spline numbers? are your spares the same?