Pulled up old 1983 Mansfield just now to see what goodies were hiding under it. I found a CI flange in pretty good shape (I think?) that appears to be soldered to the 4" CI pipe that goes straight down for a few feet. Flange is on top of the finished vinyl floor. Access below is possible but not easy.
After cleaning it up a bit I determined that the flange is good to go, but am unsure of the wax ring to use. What was there was a ring with a rubber sleeve and there appeared to be some leaked water at some point. Now this toilet would always clog, but we never had any water coming out from the un-caulked base of the toilet at any point, so I believe it was minimal leakage whenever it did occur. And it may have just been sweat too, as this guy was always dripping like it just ran a Marathon.
After research I see that most here don't like the reinforced/sleeved wax rings, but that is what was recommended at the local hardware store. In my head it would seem to make sense here since the pipe opening is a bit large. Or am I over-thinking and should just slap a regular ring on it? The ring I purchased is from an Oatey No-seep No. 3 Kit.
Which ring should I go with? Any other pointers? Test fit of the Eco Drake fits nice and will just barely need shimmed up.