For what it's worth, this was the firewall marking on my 56 Pathfinder when I started working on the engine compartment (sorry, will not be replicated, I am far from a purist - I am not about to scribble on my now-lovely semi-gloss black engine compartment)
btw I have no idea what those marks (look like H-2 to me) mean.
From left; illegible scribble single straight line down firewall to the right of the heater box 667 - 75511 9 - 29
That illegible scribble above somehow looks to be in the same style and position as below on a 67, Sometimes I swear I can see the same guy doing this through the 60's.