Technical 401 Nailhead miss

I have a 62 Buick Invicta wagon with a 401/sp400 from a 66 wildcat. Anything that can be bolted to the engine from the outside has been replaced or rebuilt. I have dual glasspacks. It has a pretty noticeable miss on idle and backfired occasionally, and it will occasionally suck a dollar bill up to the pipe when you hold it up to it. I’m guessing it’s valve/lifter related. I haven’t torn into the engine any. I’ve probably put 3000 miles or more on it in the last 2 years. Curious as to what remedies I can try before I start pulling the valve covers. I’ve heard sea foam and marvels recommended in passing but I’ve also heard not to use any solvents. Thanks in advance


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Isolate the cylinder/s, check the plug, wire etc. Do a compression test. All basic diagnostics.