Was Change Made?

Yes, there were many different versions of the small block timing covers. The factory covers had the seal go in from the back side up through the '77 model year. '78 started the seal in from the front version. They did make replacement covers for the earlier models with the later seal design too. Bolt-on timing indicators, cast-in indicators, passenger side, driver side, alloy covers and cast iron covers,......there were all sorts of versions. Just match the cover with the balancer used, or, you will have to make your own timing marks. I haven't run across any interference with early water pumps with later covers.....or vice versa, but, with "made in China" pumps, anything can happen.