Thanks again to all for your input
and to mikim, for http://www.mecha-tool.com/racer/
as I did not find that one in my search.
talked to a guy at napa that has worked there for years
he said, he was familiar with trucks and other vehicles that use GL-1 90 weight mineral oil
his advice was to keep using what was factory spec and has kept the tractor running for 56 years.
He said, he had seen it so many times over the years, someone changes the type or weight oil in one of these older vehicles and then the motor blows or other related problems start happening.
of course he had plenty of GL-1 oil on the shelf at $16 per gallon, I only need 8 gals, so I should be good to go.
Thanks again,