I have a 1961 348. The code that should be on the right front is not there, possibly ground off during a rebuild. The dip stick is on the passenger side which I think some truck engines were, don't know for sure. I'm having a problem with intermittent backfire above 1500 RPMs. I'm running an Edelbrock 1406 carb. After installing the carb I drove the car three times, about 50 miles, through our development not exceeding 30mph then the backfire began. Plugs show the mixture was way rich, black. Have adjusted as lean as I can but still have the backfire. Don't know what the timing should be, running at 8 deg btdc now. Thinking I should just run it for a while and hopefully burn some carbon out? Any advice please.