gas and octane question

Do a cranking compression test. Also I wouldn't worry about the lead additive. If you had a truck and towed or plan on driving it 100,000 then I'd use it.
My 273 has 150 psi cranking and a static of 9 to one. I run 87 and 34 degrees total timing. Never once had it ping. If it doesn't ping with the fuel you are using, I wouldn't worry about it.

Although non-oxygenated is better fuel all around. Especially if you don't drive it often and the fuel sits in the carb for a while.