Well John,unless you find a Highway patrolman that was here 30 years ago and knows the roads and things like a well read book,I don't think it's possible to find the original sign locale.
Had I been here in '74,I'd have a better chance at telling you myself. Hmmm,I wonder if it was still here in 1980? Betcha it was,darn!
What a lost opportunity!
Benn me. Later~!
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"A knight of the road,going back to a place where he might get warm."
- Borderstone