Try a set of NGK plugs.they are cheap and work.I run them in my aluminum headed 440 with 12.5 domes on the street.I also dont care for Accel wires.I run Taylors on everything.Mine with 2 inch TTIS have been on at least 12 years.My kids 413 with 2 1/8 tubes have been on 5 years with no problems.He runs my old worked 516s with NGK plugs.You migh also have a valve thats just barely burnt.Compression test would tell.Also to check timing chain.Turn crank to zero.Then while someone watches manually turn it back till the dist moves moves.I like to see less than 10 degrees on an old chain.Rocky