@SteveHolmes,
the 307 was not a great motor to start with, and has been out of production for over 30 years. and was only produced as a carbureted engine.
guessing from your choices, I would imagine you are using an old a6 axial compressor. also not very efficient...
a modern a/c compressor will use 10 or 15 horsepower away when running correctly.
this should even not be noticeable on a properly functioning V8 engine...
some intrepid folks even mounted air conditioners on old volkswagens, where 15 horses really took away from the 65 it started with...