Green Diamond is IHC. It originated in the early 30's as a Willys engine. IHC bought the design and tweaked it into the Green Diamond. It was a flathead that, in the 40's was available in 214ci and 233ci variations. In the late 30's it was available in smaller displacements, I believe. It was last produced in 1949, I could be wrong about that. Very simple engine and put in all light duty IHC's up to about 1.5 tons. Then, your engines were the OHV Blue and Red Diamonds=bigger displacement.
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