You will have improper gear oiling. In the upright position, part of the pinion gear, and part of the ring gear sit in a lube bath. which instantly oils both gears as they contact each other. From there, everything else is splash oiled.
If you flip the housing, the ring gear will be the only thing in the lube bath, the contact point will only be oiled by what the ring gear can carry, with very little lube left for cast off.
You'd need to move the vent too, but thats easy compared to fixing the lube issue.
I'd also want to check the torqure rating on that axle, Olds torque output is notorius for ruining under rated axles.