If it is original to the car, it should be a World Class T5. To properly ID the transmission, I suggest looking at a few websites:
http://garage-scene.com/t5-into-ag-body/ (look for the chapter on identifying marks)
http://www.5speeds.com/t5/index.html
The items to look for:
The front cluster bearing is a Timken bearing, not a Torrington bearing
The input shaft is 26 spline, not 14 spline
Check the 1st gear ratio to be sure it is 2.95:1, not 3.5, 3.7, or 4.0:1
Check to see if the input shaft is tight or if it wobbles (bad bearing or needs reshimming)
There is not much more you can look at from the outside.
If these points are true, than for $100, you are getting a good deal.
Will it be stronger than your Saginaw? No, they are about equal in strength, depending upon the 1st gear in your Saginaw.