For my 1951 "Babe" I got a very late start this season. She sat idle for a full year. I reconnected the battery, charged it and after checking for spark (good)because she would not start I siphoned all the Sta-bilized gas out and replaced with fresh, non-ethanol gas and cleaned the richly carbonized plugs, and she did start and ran smoothly for a 15 minute test. Two hours later she wouldn't start. Went to local NAPA for new plugs as I have done every season, for the Champion H12's but they were out of stock. Asked for the Autolite 437's but NAPA didn't recognize that number (huh?). The clerk offered AL 216 which he said was compatible. Bought'em but checked on line, found that there are 3 AL plugs said to be compatible. The AL webpage says that the end number, 6 in this case, indicates heat range, and the higher the number the hotter the plug. I could not confirm if that is the same with the Champion H12--but if so, that's quite a jump from 2 to 6, which would be a step down from a 437? I have not installed the 216's yet, pending Forum replies.
BRUCE, are you out there??
Maybe the AL 216 copper plugs are a newer version of the 437's??
P.S. Regrettably am relocating so will put Babe up for sale once I get her back to speed. (sigh)