[' What weight oil should I use?"
Good morning Buck.
Is there some reason you don't ask this question of a lubrication engineer at one of the major oil companies? Since their companies sell a full range of lubrication products they have no reason to steer you to anything other than the product best suited for your application.
I have found them to be very knowledgeable and helpful, Here's just one example of many. My street rod roadster has a Chevy Vega steering box and the recommended lubricant for that, a very low viscosity self leveling grease, has been unavailable from GM for nearly 20 years. I called Shell Oil and the lubrication engineer who took my call took the specifications of the product I needed and he cross referenced it to a Shell identical equivalent of that product. Because I was looking for an amount smaller than anything Shell sells he sent me a complimentary container of it as a "sample".
It seems miraculous to get both a product known to be the exact right one for the application and to get it at no cost, but that actually resulted from a simple phone call asking for information. I've had identical experiences when other lubrication questions came up. I'll take professional knowledge over amateur anecdotal opinions any time.
Here's a current discussion of a very similar topic on the Chevytalk forum. https://www.chevytalk.org/fusionbb/showtopic.php?tid/362566/post/new/#NEW
Notice the graph and links to additional information posted by the Moderator "Grumpyvette" To those of us who like seeing the data with our own eyes that kind of complete information is really appreciated.