[TedEaton]

The 215 Six when introduced in 1952 had the same mushroom lifters as used later for the Ford Y V8 engines. Before that, the Lincoln 337 CID Flathead used a mushroom lifter that was slightly larger on the shank diameter so it could be hydraulic (non-adjusting). The 226 Ford flathead six also used a mushroom style lifter but it's also slightly larger on the shank diameter than the later production 215/223 Ford Six and the 239/312 Ford Y. Many diesel engines also used some form of mushroom tappets if not using a roller camshaft. Ted Eaton.