I should say that my Lark 40 hp has been running with Amsoil, fully synthetic pre mix at 64:1 since 1978, but that is just me. If you want to be extra careful you can run at 50 to 1. These techs here are so great, I love these guys, don't want to "ruffle" their feathers. They are not as open to leaning down these old motors. I'll tell you what, you go get some Amsoil Saber 2 stroke pre mix, and mix it at 50:1 with non oxy fuel. If you toast the powerhead on that old boat anchor, just send it to me. I have 4 of these powerheads for your motor, they are pristine. I will send you a pristine 30 hp 1956 or 57 powerhead, plus 100 bucks for your trouble. Google up "Raquel and Tim's Timber" in Duluth MN. Just make sure you have a good powerhead to begin with. Like to see 100 psi or better on warm compression test, throttle open, both plugs out, pulling very swiftly. Remember, some models had a decompressor when using the recoil, you will have to defeat that for your compression test. Make sure you have a good rope on it.
I love to run my vintage outboards, but can't tolerate people scowling at the smoke. I don't have to create a problem and make these sweet motors a bad name. People are amazed when they witness such a great running outboard that is 60 years old. That's why I do it. This is true, reliable, trustworthy engineering. I do it to proove that.