It's really easier to figure out which tranny is when it isn't installed, because the grooves are on the input shaft.
From Patrick's catalog (thanks Jack):
No grooves = 2.85 1st gear
1 groove = 2.54
2 groove = 3.11
3 groove = 3.50
I have a pristine Sag 3 groove that I paid $50 for out of a guy's garage sale.
If it has a cast iron case, and the reverse shift lever is in the tail housing, it is a 4 speed saginaw.
