Sometimes you win.

So the short version is, I have a WD, it was at a tractor show the *boys" were running it when it started missing. A helpful older guy thought the firing order was off so they rearranged the sparkplug wires but it didn't change. They brought it home and pulled the plugs. They were fouled so we went to town for plugs and wires, it has a mag so we needed wire core plug wires and nonresister plugs. We started at our local AGCO dealer and went to 3 auto parts stores. NAPA had the wires but noone had Autolight 295 or AC45 plugs, the last store crossed to NGK plugs. We came home and put the plugs and wires on, carefully checking the firing order. When we were done it ran about the same. She had good spark at each plug so we thought the mag was working, but pulling an individual plug wire didn't change the way it ran. We pulled the valve cover to check for a stuck valve, there wasn't one so we checked the valve clearance while we were there and they were pretty good. Next we did a compression test, 1,2 and 3 were good and nearly identical, number 4 was about 10lbs less but not bad. The plugs were sooty like it was running rich but we chalked it up to the misfiring. It was left sitting till yesterday when it had to be moved. I had bought some 295's to tune up another tractor and just for the heck of it I put them in. Well it's like a different tractor. It runs like a sewing machine. The moral of the story is don't believe every cross reference chart, or use what you know works. I sure could have saved a lot of time and effort, but I'd been meaning to check those valves anyway.