I have modified a 6n one to fit before.
They have 4 lugs that hold them onto the 6n motor, the bottom right lug needs to be cut off in order to sit right. And also the standard bottom alternator bracket needs another hole drilled just before the bracket bends.
The top two lugs, with a bit of persuading with a hammer, will fit in the mount and I put a bolt through each lug.
So in the end it is held on with 3 bolts instead of the original 2.
I used this setup for a good few months with a standard twin V-Belts and everything seemed to line up ok and it worked fine.