This San Leandro, CA based company built light horizontally opposed cylinder Nelson (see) engines for target UAV use. They built the H-59 y H-63 models.

From Appendix 6: In fact, these were Nelson (see) engines. The one shown below is the horizontally-opposed four-cylinder H-63 that gave 42 hp at 4,000 rpm. It was a two-stroke engine that used a mixture of gasoline with oil and it had double ignition.

"Barmotive H-63"