I don't recall taking off the rear brace (398887) for the alternator is it possible it was running without it?
It looks like the alternator will mount fine without it.

 

The car will run if you leave off the air cleaner also...

Look, GM did not put unnecessary parts on these cars just to reduce profit. The brace is there because without it there is deflection of the alternator towards the water pump due to belt tension. This causes fatigue that will eventually cause cracks in the remaining bracket. There was one there when the car left the factory.

 

What year is that bracket off of?
Where does the brace attach to the engine?
What engine??

I'm having an alignment issue with bolting up to aluminum heads........

 

Since Oldsmobile did not offer aluminum heads as a factory option, there probably will not be a factory brace that will bolt up. A good fabricator will be able to make a brace for you that will look and function like factory.

 

That style of bracket looks like it will work. Have you got one?
I'm the fabricator.....so I get to engineer and manufacture the brace, but I need the alternator in place first to do that.!
Thanks.

 

I would think a little time spent with a grinder would provide the clearance needed. The other option is to swap to the later year brackets. That’s what I’m using on my car, they fit and function just fine.