Looks motorcycle to me, but, it's a tach, it's vintage, and it's cool as heck!!!
Yes it is a cool one Geof, but the RPM's are to low, I think most motocycles went to 10 G and up, even back in the 70'es. Just thinking out loud while this Denver Bronko game gets started
:drinkers::drinkers:
Marine....................
http://www.classicboatwork.com/classicparts/gauges/othergauges/other.html
Marine....................
http://www.classicboatwork.com/classicparts/gauges/othergauges/other.html
if it's marine, bear in mind it might also be for an outboard (two stroke, magneto points triggered) and useless for a v8. In fact, hard to say how many cylinders it might have been for, anything, lol, from 1 to 12