Adding new alternator

The stock alt. is 36amps. I'm putting in a MSD Pro billet ign. system (360engine) and I think I'll need more amps. I thought that approx. 80a would be a good output for me to get. Delco 12si is 78a. I could get a Mopar alt. but the one on my 71RR (60a) does not have good output at idle where the Delco's are known to have good output at idle. So, I'm having a hard time deciding which one to use. However, the 36a in there now does not have a problem with output at idle.