Difference between 1967 and 1973 alternator on Small block?

Pulleys and brackets changed from the '69 and older version to the '70 and up version.....both A/C and non-A/C setups. The alternator pulleys came in a few different diameters and in a single (non-A/C) and double (A/C) version. Usually, the double pulley will work on a single pulley application.