Spark plugs for GT40P heads ?????????
Recomended plug for GT-40-P heads = Autolite #104.
Recomended plug for GT-40-Y & X heads = Autolite #764
I have used the #104 for a year on my P heads without a miss.
1994 Ranger Splash 5.0 HO, Reworked AOD, 8.8 Diff w/ Moser Axles, Auburn Locker w/4.30 Gears, Balanced Rotating Assembly, FRPP Crank, Scat Rods, 10.1 Forged Speed Pro Pistons, P&P GT40P Heads, F303 Rllr w/1.7 Rockers, Air Gap Man w/Demon Carb, Hookers.