This is a bit generic out of one of my collection of text books but it does explain it fairly simply.
Have a look down the bottom of the face, it may have the meter movement type. It will read something like 1000uA , (1000 microamps), or 1 mA (1 milliamp). You can buy replacement meters with the same movement rating, then you can re-calibrate the scale or you might be lucky and the numbers printed on it can be used directly. Sometimes the rating is printed on the back of the meter casing.
I think if I had a mixed breed hunting dog, but I wanted to impress people that he was pedigreed, I'd tell them he was a Blue Point Growler. Maybe throw a state name in there too, like Kentucky or Arkansas. "I ain't never seen a dog like that before." "You ain't? Well that there is a Blue Point Arkansas Growler!"
Thanx! Another site that it looks like it might be worth bookmarking! Weren't these growlers also used for testing generators?
As a former Snap-on engineer, I think you may have all there is to offer. You can call Snap-on directly and explain to the nice lady that answers the phone what you need. If it's available, she will know who you will need to talk to. Don't know who actually built the MT326. Snap-on had their own electrical division and bought Sun a bit later. Snap-on brand was made in Algona, Iowa and Sun in Crystal Lake, Illinois.
Tubalcain's YouTube video's as the one above is awesome. Whether it's his lathe videos or this one, he pretty much covers it correctly. I highly recommend his model specific lathe videos.