MikeE,
A saginaw 4 speed is not the same as an SM420. An SM420 has synchro 2,3,4 with a non synchro 1st (Granny Low) and Reverse.
We have been discussing the saginaw 4 speed which relatively speaking is a close (closer) ratio transmission used in mid size (and compact) vehicles from the 60s-80s. Patrick talks this transmission up as he spent a ton of time and money developing products (Torque Tube tailhousing and shifter) for it before cheap ODs were readily available.
That being said, the 3.50 first and 3.11 first saginaw transmissions offer excellent ratios for our trucks to keep the engine in an effective powerband while still allowing you to use them as a truck with the good 1st gear ratio available, especially if you have 3.38,3.42,3.55 or 3.73 rear gears.
