My car is a 73 'Cuda 340 with factory air.
Are the two belts that run the A/C and the Alternator the same size? I replaced all 3 belts today, but the belt on the pulley closest to the alternator seems to be loose, and sitting "down" in the pulley groove while the other belt is very tight. There is no problem wuth the power steering belt.
I'm thinking that if the belts are the same size then the alternator pulley might be worn out.
Yes, they should be the same. You normally have to replace them both at the same time. Make sure both belts measure the same and their cross sections are the same. It's possible that the wrong belt was put in the package.
Back in the day you could buy matched pairs, tied together with a string. They were cut at the same time. Not done anymore, 2 belts with the same part number can be as much as 1/2 different length.