gas engines? i can only comment on the ford stuff..
F150s... the 04 or 05+ got the 3valve heads and thats the ones that have the sparkplugs snap when trying to remove them unless someone changed them or added antiseize early on...
F250s+/superduty trucks with the 5.4L got 3valve heads in 05 i think, don't quote me on that, were basically told a high mileage 2007 F250 needed a whole engine because shop couldnt get the last 3 plugs out, or pieces of them... Had a neighbor finish the job for $400 and truck is perfect now.
Ford Trucks, Simplicity machines, John Deeres, Ferris mowers, Stihl/Echo/Redmax handheld equip. lots of trailers