there are a few identifing features
most have an Alum case but the early ones did use cast
all had the double shift mount & 95% of the ones I have seen didn'1 have the rear shifter pad mount drilled
the front brg retainer will measure 5.2" diameter , these can be milled down to the more common 4.80 diameter
the front shift lever will point down fron the retaining nut not up , all ODs were pointed down to reverse the shift inside the tranny , all non OD were pointed up
the last way to check is to shift it into 3rd & turn the input shaft , the output shaft will be turning significantly faster