My 1967 Chevrolet Service Manual on page 3-10 says Steering Knuckle/Steering Arms should be tightened to specifications.
When I look at the specifications sections, I can't find the torque value for the 2 bolts holding these parts (and backing plate) together.
I know anchor pins is 130 ft.lbs.
Just to be on the safe side, I'd like to make sure it's tight enough...

Edit : is it well Steering Arms attaching nuts at 85 ft. Lbs.?

 

When a factory manual says torque to spec and no spec is given there should be an appendix section that will list the thread size and torque as a standard. You just need to know the major diameter of the threads, you may need to round up a little. Example: If a bolt measures .480” across the threads it’s a ½” bolt.

Some non-GM manuals copy this word for word out of the factory manual and do not have that information in it. You can also find standard torque specs online. If in doubt I would use grade 5 as a middle of the road spec. Outside of the body bolts there are very few grade 2 bolts and Outside of the motor there are very few grade 8 bolts.

Quick observation, maybe I am thinking of the wrong bolts but your torque specs seem very high. Even with a grade 8 bolt 130 ft lbs would a 5/8” or ¾” thread. Over tightening a bolt is worse then not tight enough long term, assuming the error is proportional. But after saying that some bolts are very spring like and they are designed to be streched.

 

I have a chart of torque per thread size on the wall in my garage but I prefer to use some specs as we may have something specific...
Then anchor pin at 130 ft/lb is a lot but it's well what is in the manual.
Also 85 ft/Lbs for the Steering arms seems correct for the thread size although I did not cross checked with my chart !

 

If you have the factory manual and there is not direct stated torque then the chart in the book is the only option. Anything you find on the net is just someone looking that up or giving an opinion. It is possible that GM could have released an addendum to the manual. They use to have little add-ons but those usually that was just for errors or revisions. As long as there was not an issue's with stuff coming loose it would not be updated. If the part is aftermarket then maybe the aftermarket manufacture would have something?

There are a lot of things that make up the optimal torque of any thread. Material and Material tensile strength, thread pitch, quality of threads, mechanical design of mating components. If you use a chart all you are saying is you don't care about most of that and all you care about is that the thread area stretches with out getting close to yield point.

There is more accurate ways of tightening a bolt that involve a dial indicator high quality studs and a math formula but that is normally limited to high performance engine building.