I took a quick look at the bike and it looked well maintained, but ended up being a 25" frame. The guy I talked to is selling it for his father, and I get the feeling that the father was or is a bike guy/curmudgeon. So the measurements I got through the son were a 23" top tube apparently, because that's the one that matters. and when I did get a reported measurement for the seat tube it was 24" which would be the center to center measurement.
I didn't give it a thorough check, as I wasn't going to buy it, but I did get a 36mm-ish measurement at the chain stays, So it looks like the bike might take 28-30mm tires.
Here's the listing:
Miyata 710