What type of alternator are you using, race or street car? 440 right? I had a 440 with Indy heads and a CSR water pump and using a Powermater alternator I was able to fabricate a low mount using an adjustable heim joint to brace and adjust the belt tension on the lower part of the alternator,I used a stud in one of the mounting holes for the timing cover near the balancer as the mounting point. I also used the tapped holes in the front of the cylinder head to support the top mount of the alternator and supported that with another adjustable double sided heim joint.

I do not have a picture of the lower mount on anything here in Iraq, but I do have this engine shot that gives you an ideal on what I did. Hope this helps