Small block 727 inspection covers

I have two different inspection covers that fit on a small block 727. One is a one piece full cover. The other is two pieces, the large cover with the little piece at the bottom center. Was there a change from one to the other in a specific year?

The 2 piece cover with the small opening was to drain the torque converter when servicing the trans. not sure what year the did away with it. My guess would be in the 70's but not sure on that

My ‘72 has the galvanized 2-piece cover...

The factory parts book show the 2 piece shield until 1979 and 1 piece for 1980 and newer. This is for both the 904 and 727 trans.

Thanks everyone.

The drain and that two piece cover went away when they started using lock up torque converters. I thought I read somewhere years ago that it happened in 79 but it was somewhere in 78-79-80.