I purchased an eco model 94 and when I was checking it out I noticed a painted over label on the side of the wall mount bracket. After I cleaned it off it turned out to be a brass tag that was glued on that reads: BUICK MOTOR DIV. GEN. MOTORS CORP. MACH. NO. 122636. This is stamped or engraved on the brass. The serial number for the meter is 4 N2721 spec. no. 94 1001.
I believe it may have come out of the GM proving grounds in Michigan since the previous owner was imployed there many years ago. Anyone ever seen one of these?