I would find it od to se a mechanically driven tach in a truck. Those were more of a Corvette thing. However, if it were a mechanical tach (unlikely), it would have been driven off the distributor, which is specific to a tachometer drive. To my knowledge, there are only 2 tach drive distributors, both for Corvette use. 1 is the regular tach drive,used in both small and big block engines, and had both a points and electronic breakerless (late '60s RPO K66 option) operation, depending on application. The other one was only used from '57-'65, and was the Feul Injection distributor. It had, in addition to the tach drive, a second drive that ran the high pressure feul pump for the Ramjet Feul Injection. Those were matched to the manifold, and serial nubered with them. Very rare, and very pricey if you were to find one.
50 series truck is a medium duty truck and some applications would or could have had a mechanical driven tach depending on eng
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