I've got a Haynes manual that states the gap should be .035 but I've read here that stock is .040. I'm wondering which one is correct.

 

I have a sticker on the rail near the radiator under the hood that says .040. I don't know if it's the same for all years.

You could increase the gap for an MSD ignition.005 increments until you get the best burn, an if you run nitrous or are supercharged, you might want to decreaseby .005for quicker spark and less chance of detonation.

 

Thanks

 

0.035 for the 1992-1995 engines with Champion RC12YC or substitute the earlier 9 heat range plugs used in 1992 Jeeps. (see Magnum Engines Sparkplug FAQ)
0.040 for later Champion plugs with longer noses

The Ram Magnum engine ignition system with new parts is pretty good and can fire up to 0.065 if the sparkplug edges are fairly sharp.
The iridium plugs can probably fire with even wider gaps.
The idle gets smoother with larger gaps and rougher with small 0.020 gaps