I contacted Briggs & Stratton, which manufactures engines for the SAE Supermileage Competition (2-10 horsepower range) to find out if they had a hydrogen conversion. They said they did not have the expertise to produce alternative fuel engines and only sold diesel, gasoline, or methanol engines. I've read that the people who work on hydrogen storage also have expertise in hydrogen-burning engines - they have to be well-rounded to sell their primary product. A couple of these companies are:

Millennium Cell
Fuel Maker Corporation

They have developed both liquid sodium borohydride hydrogen storage, and compressed hydrogen storage, respectively. The success of their product depends heavily on the future development of fuel cells by automotive companies, and their acceptance by consumers.

I also found a new method of producing hydrogen on demand that requires no special storage at all. I found this website:

Hydrogen on Demand

Two aluminum electrodes are immersed in water and are discharged with high voltage. The discharge generates sufficient heating to form a metal oxide, and liberates hydrogen from the water. This method liberates only enough hydrogen to power an engine or fuel cell, and therefore eliminates the need for heavy storage tanks.

This is very curious technology, does not seem any less convenient than the methods used by Millennium Cell or Fuelmaker Corporation, while at the same time completely eliminates exotic materials and any danger of explosion, fire, or toxic reactions.

Completely new to me. Opinions?