Production years for G and H 6 cly flatheads?

[amodel25]

The G engine has a crab style distributor on the front of the engine. The H has a conventional distributor on the driver's side.

M engines were installed '49 to '53 in F-6 and larger trucks. My research indicates that they were used in School buses during the same years.

The M engine has a 3.5" bore where the H has a 3.3" bore. Both engines have a 4.4" stroke.

The M has heavier H beam rods, a stronger crank and more support in the bottom end of the block. I haven't tried but I am told that all internal parts between the engines are dimensionally interchangeable except pistons.