Originally Posted by
prairiepedaler
If I decide to bag a Multi-track, which model would be the one to go with? Usually, a 23-24" frame with a 23" tt works well.
To add to what
ksryder said above, the geometry of the various 7xx series frames does change a little bit with model year and with specific model line (730 vs. 750, etc.). The Vintage Trek website has a lot of great information about these older bikes, including catalogs and technical information from the era from which you can get geometry data.
For example, I have a 1997 750 and its geometry is relatively "square", meaning the effective top tube and seat tube measurements are usually pretty close. A 23" frame has a 22.8" effective top tube. The frames themselves had the same relative measurements in 1997, but the 730/750 forks have a 50mm offset whereas the 700/720 forks have a 40mm offset (so the 730/750 have less mechanical trail than the 700/720 do).
You can pour through the Retail Tech Manuals available on the Vintage Trek website to see what model years and sizes you may be interested in. You can also study up on how to identify the bikes through the years based on color and graphics styles.