L31 crate engine on regular gas?

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I put an L31 crate engine into my 62 C10 about 800 miles ago. It has an HEI distributor, aluminum intake and a Quadrajet. I’ve been running premium since it was a brand new engine, but the other morning I filled it with regular, kind of by accident. When I turned the truck off when I got home, it dieseled for a few seconds after I shut it off. Everything I’ve read says an L31 should be fine on regular, but originally the L31’s were fuel injected. I think the engine has a compression ratio of 9.1 to 1. Should I be able to run 87 octane in this engine? If so, what can I do to stop the engine from running on? My idle is about 700-750. Fortunately it is a manual trans so I can stop it by letting out the clutch.
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