Just removed what I believe is the original toilet (home built in early seventies) from the main floor bath to install a Drake. Flange and surrounding tile floor are rock solid with zero sign of leaks.
Surprised to find the flange is above the finished floor and not screwed to the sub floor. Top of flange is a bit more than ˝” above finished floor. From below the cast pipe going to the flange is adjacent to and securely strapped to a joist and near a junction with the pipe from the upstairs bath. It’d be a job to lower the flange. Set the new toilet in place and it doesn’t rock, that’s got to be good.
With the old toilet there was a paper thin layer of wax on the flange with very little squished out around it, far less wax than in the “standard” ring I was going to use. Do they make a thin wax ring for situations like mine? Should/could I cut down my wax ring?
Wax could go either way...it's likely that over the years, that which squeezed into the drain path just eroded away. I think you'll be fine with a standard wax ring.
The flange could be reset to be where it's supposed to be, but not all plumbers actually do leaded flanges any more. As long as the toilet doesn't rock, you should be okay. It it's really sitting porcelain to metal, you need to address this, or you could have a catastrophic failure.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013