Its hard to go by the old specs, if you consider that the oils they are recommending have been obsoleted a dozen times, the oils that were cutting edge in the 60s, 70s, 80s...are not even available. Like 2 strokes, a 60s saw will say...8:1 fuel to castor oil, or 10:1 fuel to Sae30. We dont need to run a heavy mix to protect an engine, we have excellent oils that are safe to 70:1 and even 100:1. Motor oils of today are a marvel compared to 60s/70s slop, the old standard of SAE30 has mostly disappeared from all manufacturers, briggs was a big holdout but even they now say 10w30 or 10w40 is fine...and it makes sense, a multi-viscosity oil gives you the thinner qualities when cold, but still protects like a heavier oil when hot, its not holding you to a compromise with straight viscosity. Ive been running Mobil 1 Full Syn 10w40 in 3 FD Kawasakis, 2 Kohler Ks, 4 Onans, 3 Commands, and T6 Syn 15w40 in the Yanmar for a long while, no ill effects. I had to swap a broken cam in one of the Kawasakis at 991hrs (plastic gear) and the engine was spotless inside.