I would suspect those holes are for the pulley neutral balance. The holes to bolt it on the balancer are evenly spaced, so any special balance would go out the window once it was removed, unless it was marked for position.

That time frame was pretty bad times at Chrysler, they did a lot of strange stuff just to put a car on a dealers lot for sale. Over the years I've seen a lot of strange stuff that caught my eye and made me ask why, but the things in question still functioned, so there were soon forgotten. I could easily see them having a bunch of out of balance pulleys they bought at fire sale prices with the "custom" pulley balance for the correction, where normally they would have rejected them.

90% of the customers would never know, and most of the mechanics wouldn't care as long as it worked and didn't cost them money to correct. Really, until guys like us started collecting this stuff and started asking questions, it was probably only known by a tight circle of upper level management. We are now guessing why it may have been done.