Jack,
You might have opened a can of worms.
In the late 60s, I was also told to use non-detergent oil in a 216 and a high-pressure 235. However, by the time the high-pressure 235s were introduced (1953/54), GM was recommending detergent multi-grade oil.
GM was also recommending detergent oils in earlier years, for hard-working engines.
Your 10-30w (10-30, 10W-30) oil is OK.
