First, I want to thank Jim Cepek who did most of the legwork here back in Nov. of 2006. Jim has an "M" series Ford flathead in his Funk, and I have an "H" series.
Reference from "http://www.48f-1.com/flathead_page.htm"
"The Flatheads came in either a "H" or a "M' series. The "M" series was more heavy duty with a 254 engine compared to the "H" series 226. The torque of the "M" series was 212@1200 RPM while the "H" was 180@1200 RPM's. The H-Series was used in the F-1 through F-6 models while the M-series was used strictly in the F-6 model. The F-7 and F-8 used a "E" series motor. . "
Here's how to tell them apart:
H Series - marked on top of the head (between spark plugs 2&3) in raised letters "1HA-6050", and on the left side of the block, down low, "1HA-6015"
M Series - marked on top of the head (between spark plugs 2&3) in raised letters "8MTH-6050", and on the left side of the block, down low, "8MTH-6015"
Please note that additional suffix letters or numbers may be present - my block is actually marked "1HA-6015A" and Jim's block is "8MTH-6015B 6" I do not know what the additional numbers and letters mean.
Posting not permitted in the forum archives.