spark plug heat range questions.

It will be interesting to see the responses you get just because you have so many variables that the answers aren't textbook. You may have to just tru a couple heat ranges colder and hotter to see what results you get. I had a similar problem when I rebuilt my 273. The compression went from 10.5 down to 9.6/1 and it never ran right. I tried 3 heat ranged hotter and the idle miss cleared up and it runs , well like a new engine. I was using Autolites but went back to Champions. Good luck! tmm