The ACS moved from the 3.2.x codebase to 3.4 and from there to 4.0. (And from 4.0 tcl to 4.0 java and now 5.0 java is being worked on.)
OpenACS did branch from ACS 3.2 around the time arsDigita itself branched to 3.4. OpenACS 3.2.5 has various improvements over the ACS 3.2 codebase, including backported features from 3.4. However, OpenACS development is now concentrated on porting ACS 4.0, and is apparently going to be very faithful to the ACS sources.
