I have the same issue only with a hotter than stock 302. I has been that way since the engine was installed many years ago. Typically, it happens at car shows right after I register and try to move it to the appropriate parking area. Gives the other car owners a chuckle at my expense. I have tried a bunch of stuff including changing to an Edelbrock carb, electronic ignition and wide variations on timing. Nothing has made it better. My next step is to try a colder heat range spark plug. Shouldn’t be much of a problem on those occasional cold mornings here in Florida but I wouldn’t want to try it in the cold hard North. I will be watching the advice on this topic with interest.