What's everybody's favorite spark plug for a basically stock 383 RR?
This thing has a Rev-N-Nator ignition but the RJ12YCs are really sooty. Normally I'd just go with a stock Champion but thought I'd ask.
(Yes, it appears this thing needs some tuning, but I'd prefer to baseline the plugs first.)

XR5 NGK

std heat range autolite....

very reliable.

Sounds like todays fuel is to rich for your motor, try leaning down, increasing in diameter, the primary metering rods by .002 to .004 on the big step

Cab, the car came from about 4500' elevation. Haven't looked at the tune-up yet but will after plug change and some snooping around.
(Too damn cold this week to open the shop door and run the thing)
Only time I've lit it off it seemed kinda lazy, like not enough timing, didn't smell rich though. No idea how long the plugs have been in there.
I'm at 2500' with usually 100%DA, FWIW.

The age of the fuel can have bad effects and will determine how it burns in your motor, bad fuel=bad results
I have a local customer who is dealing with that here now on two cars he doesn't drive very often or for any long trips to use the old fuel up.
I recommend draining the oldd fuel and put in some car or truck you drive to use it up or dispose of some other way and put new fuel in it, I go to the local airport and buy 5 gallons of 100 LL for my Dart GTS H code 383 4 speed car when it is going to set up here in the garage during the winter after running the fuel tank down really low before parking it. I put any fuel non leaded out of it, if it is more than 1/4 full, into my wifes Camry or van

Yup Cab, I hear ya there. Has fresh gas in it now. I'm also gonna do oil & filter and check that out, as well as verifying dipstick.
I've been putting old gas into my non-cat plow truck for years, it seems to digest anything, haha.
I'm gonna go with the NGK XR5/3332, which NGK says should be gapped at .039, rather than the resistor Champion.
I haven't heard back from the Rev-N-Nator guys yet, but from what I've read they say to pull timing OUT for their box, and usually to disconnect the vac adv, which I'm against doing for a street car. VA is connected on the car, but the hesitation when blipping throttle seems either insufficient timing or pump shot (AVS). I'll know more of course when I can run the thing and put a timing light on it.