I searched the forum and read what you stated, Evan....The ribs were only on the 998 and 999 versions. The date code (if I could ever determine it) would determine if it is in fact a 1980 and newer case. The information varies from source to source as to the exact date that the 2.74 1st gear set was installed and when the 2.45 gear was discontinued. I thought that by the early 80s, ALL of the "904" style transmissions had the low gear set and lockup converters. I had one in a 73 Duster in the mid 90s. When the trans was going out, the lockup would stay engaged even as I slowed to a stop. The car would shudder and shake until I popped it into neutral. This somehow unlocked the converter and it only seemed to re-engage as I shifted to 3rd/drive. I got that transmission out of an 80s Diplomat or Gran Fury cop car.