Actually, in the early 80s I worked at a production engine shop, installing the new engines in customers vehicles, and at that time we did quite a few 360 & 390 Ford PU trucks, as well as some 330/361/391 FTs in cab overs, Louisvilles and 5 ton style F series trucks. I did several 75 &76 Ford pickups, and was suprised to see that there was new reinforcement ring for the flexplate bolts, and the bolts themselves were a bit shorter. So perhaps, towards the end of FE production, they stopped installing the rings? I do know that I seen enough of them that it was unlikely that there were this many that had the rings removed during say a transmission rebuild.