I put an aluminum cover on a 8.6" GM. There were a few things that needed to be dealt with, most due to the increased thickness of the aluminum cover, and the presence of the stiffening "fins".
The original bolts didn't fit the new cover and I didn't care for the ones included, so I had to find some other bolts.
There was an emergency cable bracket that bolted underneath one of the cover screws. It's shape wasn't completely compatible with the aluminum cover so I had to ground down the bracket a little.
Unlike the OEM, the aluminum cover had no magnet. I chose to add a small magnet to the drain plug.
So it can be considerable work to install one of the aftermarket covers.
Knowing what I know now, I probably wouldn't bother putting one on a non-LSD (clutchless) diff. For the clutch type LSDs, I like to change fluid more often and it is nice to have the drain plug and avoid the need to remove and re-gasket the cover with every oil change.