its an 8 inch from a 65 mutang, I think they have a drain plug in the back of the case.
also the tube comes out of the centre portion and tapers from 70mm to 60 at about 190mm = 8 ish inches
if its a mustang 2 case, the tube comes out at 70mm but tapers to 60 much sooner - about 3 inches
/\ mustang 2 case
as said above, the brakes are finned nine inch internal diameter
the bolt pattern is 4 on 108mm
the bearings are the same, but the layout of the retaining plate differs.
the 5 lug nine inch internal drums are from the ford ranger, bronco 2 and aerostar.
i think the stang 2 is 56.5 and the mustang 65 is 57 inch wide, they are both centred pinion axle small bearings 28 splined.
the mustang 2 rear bearing housing is unique to the 9'' brakes
note the 4 holes-retainer, are not layed out 'square' like that small bearing 10 inch brakes.