Not an expert but I think the aluminum OD units are from mid-70s A-Body cars. Shifter is in the wrong position for your B-body but may be able to change the tail shaft housing (and shaft?). one of the pics here show where the shifter mounts are for the various cars. http://www.slantsix.org/articles/4-speeds/ODA833fourspeed1.htm
If you have one shift mount pad on the tail shaft it's not the one you want. If it has two shift pad mounts, even if both and not drilled and tapped, that is the B/E/C/truck application