It's a Model 80. I no longer can remember all the differences between the various numbers, but usually it's saddle width and height over the rails (some models like the 88 had rails that were less tall which made the whole thing lighter but were less tolerant of drooping leather). The 90 is wider than the 88 and the 92 is the widest. The 88, in addition to lower height, had an aluminum cantle, also to save weight.
The guy who commented about the ride of the dural rail models being uncomfortable is right. I had a couple of these over the years and they have no flex--the flex is dependent on the rails much more than the leather and these rails don't flex at all. It's like sitting on a cement block. Another problem with these is that Ideale had to use a different setup to retain the tension bolt, and this version takes up much more of the bolt (it's much thicker), yet they still used the same bolt as the steel railed models. Result: very little room to take up tension. Once one of these starts to sag, it's over. There's no saving it. Not enough bolt to take up even a little slack. I've got one in such a state.
On the T and B on either side of the oval--those are the initials of the company. Originally Tron & Ballaird, later Tron & Berthet (after the founders had died).
Here's a good link for the whole story: http://www.ebykr.com/