I have a set of ram horns and the driver side alternator mounts that bolt on to them for sale. I pulled these from a 62 chevy that had a 307 installed in it. standard trans.
The ports are 2.5" where the the donut mounts to the flange and all studs in tact.
I have another set of ram horns with a different style bracket mount on the 67-72 parts site.
part #s
3747038=RH
3749966=LH
80.00 plus ship on the ram horns
alternator brackets 25.00 shipped, 18.00 if picked up with ramhorns