Very good explanation. Actually, Valvoline dino oil is SG, and available generally for about 4 bux a bottle. Castrol4T is SG also. I run either in the Monza and MZ.
In the Mighty Scura and Aero engine, I run MOtul 10-60. Around 11-12 a liter, and SG rated, also. I, personally can't see not running an SG oil in our flat tappet engines.