The following has some good info concerning Champion spark plugs & indexing.
dodgeram.com
(look for Frames/tech/repair & DIY/spark plug notes & spark plug indexing)
Good info concerning heat-ranges.
Champion used to have good info on the web., but since their purchase by Federal Mogul
have been unable to find it.
My '84/RC/360/auto/Edelbrock 1905/3" exhaust/ Mopar Performance Dist & Orange box/Msd coil & wires, spends it's
life pulling a horse trailer and hauling G. Sheppard dogs for volunteer serach & rescue using '85 octane gas @ an altitude
of 4000- 6000 ft.
In my Quest to break the 10 MPG barrier I've tried the following; Champion, Autolite, NGK, & Bosch. This 360 apears to eat
the copper truck plug. Had # 5 quit firing with an Autolite 4 # 65 resistor. At present have Rapidfire #4's @ 0.04 installed.
Have had no problem with the MSD wires, but with the price Summit charges would you expect any?