Got a local source for a complete A/C system that came out of a '68 Cutlass with a 350. Will it work on my '72 U code Supreme?

 

Mostly. The firewall-mounted HVAC boxes will bolt up. The 1968-69 dash control head is different from the 70-72 control head. The ducting to the dash outlets is different due to the differences in dash design.
The compressor brackets are all the same. There are two sets of holes in the brace that runs from the compressor to the stud on the water pump, one for SBO, one for BBO. The alternator brackets changed from 71 to 72. The early ones will work, but they will not be optically correct.
Condenser and mounts should work.

 

Thanks Joe.. I'm mainly concerned about the brackets. My alternator is on the driver side so dunno if that makes a difference. Also, I have the long bracket that comes from the water pump. If I use the '68 compressor, is it date coded?

 

If your alternator is already on the driver's side, then that was originally an A/C car, or at least the brackets are from an A/C car. I can't say that I've ever worried about date codes on A/C compressors.