I see four side cover bolts, and the GM logo with a part number cast into the case all with the pics he posted, (the shifter linkage is also way wrong and the as for the reverse being left down case doesnt even have any resemblance of a ford or saginaw) instead of left up, that can be changed with either the shifter, linkage or the gears, but his explaining the shift pattern was sketchy. the best thing to do is to get the part number. Its on the passenger side at the top right above the GM casting.
take note on this trans that the lever on the side cover for reverse is pointed up, which would mean that reverse would be located left up, while the one in the z is pointed down, which would make it left down.
edit: after looking at pics on google, the reverse linkage isnt on the tail shaft, its on the side cover making it a saginaw 4 speed.