Just run NGK B6HS and see what the plug looks like ( best to go colder than hotter ) .... IMO, Champions are all togther junk, Autolite is good in 4 strokes, but NGK seems to run the best in 2 strokes.
I'm pretty sure the #456 Autolite is the plug my '65 Rambler took, which is actully a fairly hot mower plug....
funny thing with that car... Briggs and Stratton made the ignition cylinder for it ( most anything GM, AMC or International had B&S locks from the 40's- 70's ).. The keys had " Briggs And Stratton " on them.. funny to tell people Briggs and Stratton made the engines... my '51 Chevy is the same way, so I do the same thing with that..