To clarify, the 939 has a 20" bucket, 12" impeller, and it only shoots 40' when the snow is unpacked, fresh and dry and cold. It does not shoot EOD 40, but I've never had it bog and I usually hit 1st pass with momentum and then subsequent 1/2 or 3/4 passes depending on conditions. Perhaps bucket size comes into play for EOD. Does your MTD have adjustable engine mounts like a Murray/Craftsman? If so that could make a swap a lot easier, you can get by without e-start espicially if you garage it. That leaves only fuel delivery and pulley issues to sort. Don't use a steel tank. You'll have to get the PTO shaft in approximately the same position as the L head for the sheave clutching to operate properly. If you have the storage space, you stow the Tec, could experiment and then reinstall the L head since it still works. If the Tec is already verified operating at 3600 rpm I probably wouldn't mess with it, but it might get an extra half horse by bumping it a couple hundred rpm. The impellers are designed to work at a certain speed though.This is on an MTD 24 " with a 12 " impeller. The engine runs/starts well and has maintenance, so the thinking was it is not down on power due to a problem. I never had it throw snow 40 ft , so maybe there is an issue. Could be a good idea to rebuild the carb and check the governor setting at this point eliminate those as a possibility. Replacement of carb the emulsion tube o-rings is probably needed since they are trouble prone.
Any idea what max rpm for this engine? I can't find it in my tec books. It is usually 3600 rpm, but I want to be sure.
The swap to the HF will require a few things. A 3/4 " to 7/8 " shaft bushing and new mounting bolts. The bushing should eliminate the need for new pulleys and belts.