Hey Daren, here’s a link to a particularly good cue of his from Petticoat Junction, which features his “melodica” at 1:05 http://youtu.be/0_lBZ-F28xI.
I have a good lead that suggests it was actually a Clavietta, but I’ve yet to confirm it. Massey was heard on radio, tv, and recorded extensively in his own home studio, a little unusual for television composers of the 1960s, prior to the advent of the digital synth in the 1980s. A multi-instrumentalist, he played piano, trumpet, violin, and various instruments besides the melodica, and built up his tracks by playing and recording all of the parts himself. Nevertheless, it’s a great idea to see if any of the engineers he recorded with are still living. Thanks!