Going from threads on other websites, the next generation compressor, the A6 is a good replacement. It was used from '62 to as late as '85.
As early as '63 Buick was supplying an A6 unit for compressor replacement on '58-'61 full-size models. That one is a part no 6550151. I am assuming that one had mounting holes to match the original A5 unit.
Lools like the the guys who have used typical A6 compressors have had to fab new mounting brackets for it. Apparently a pigtail adapter (still available) connects the plug on the A6 to the A5 harness.
There might be some chance your car already has an A6 on it if it ever needed a new compressor. Attached is a picture of the A6 from the '62 shop manual (11-33). For comparison is a page from the '61 manual showing the A5 (11-58).
What has been, can be again. (Bob Wills, 1942)