Single alt belt to two belt question

1974 318 with single alternator belt and power steering pump. Stock pulleys and locations. All work perfectly for the last 30 years.

I just ordered the sandine 508 ac compressor with dual v belt grooves from Classic air and the proper brackets to mount it. The tech told me to use only one belt. The single belt will run the alternator, wp and the ac compressor off the crank.
To me that’s a lot on a single 1/2” belt. All I see is stretch and belt replacement monthly.

Does anyone know or have done this conversion to alternator, crank and wp pulley to dual so there are two belts driving instead of a single belt and we’re sucessful?
If so- any idea on what engine combination I should be looking for so I don’t end up with a box full of unused pulleys from eBay?

Thanks-
Joe