The original torque specifications, (for the cylinder head), are "very tight".
I usually use specs from 1940's and 1950s manuals for the same diameter, thread pitch and, (preferably), application.
There are lots of charts. I'd be inclined to use the specs for grade 5 uncoated fasteners.
I'm not a big fan of Fastenal but here's their chart.
https://forum.esk8.news/t/fasteners-what-they-are-whats-in-your-kit/4664/42?page=3