What does the OHH designation mean? Over Head Horizontal? Overhead horizontal heavy duty?
"OHH" should indicate that it was a XL series. The O indicates it was a overhead valve design. HH indicates XL series, which was the Tecumseh commercial/industrial engine lineup. Usually this means it has a ball bearing crank, industrial "kleen-aire" poly pre-filter/paper air filter setup, and possibly a cast iron sleeve (don't quote me on the cast iron sleeve). I believe it was the simple "OH" that was a overhead valve engine without the bearing on the PTO, all aluminum block, and standard accessories.
In the standard flathead H series, HH indicated it was a cast iron block engine. Tecumseh seemed to change this rule of HH's being cast iron when they started making overhead valve engines sometime in the 70's...the OHH's I have seen all seem to be aluminum block engines.
Please post some pictures if you will, I haven't seen too many of these and would be interested in what it looks like. What equipment did it come off of?