Sticks in my head that
@bozvaliant made an alternator fit without cutting the rail. Maybe he has some input?
I just tried fitting an alternator to mine end of last week and was like an 1/8" from fitting. I haven't looked up the alternator yet, but it is a borrowed one from my brother. The reason I want to look it up is to see what the amp rating is as I think there are a couple of size options and a smaller one might make it work.
I should note that the trans isn't in the car anymore so the engine angle might not be right either. The back of the motor is supported but I didn't check to see how close it is to the installed angle.