Can anyone I.D. this 'speedo' for me?

Gauge that is. My Grandfather gave this to me, but he can not remember where he got it, what car he used it on, or when. Any parts gurus out there that recognize it? Can you tell me anything about it? Thanks!

 

could be 55-59 GMC, the blocky numbers look right, and the size/shape looks right.

I'm only about 75% sure, so do some more checking

 

Was manufactured by Stewart Warner, but can't tell you who they made it for. Looks like a truck, though.

 

Thanks! That helps a ton....I'll just jog my grandpas memory with those bits of info! I appreciate it.