BMC Pro Machine SLC01, Specialized Globe, Burley Rock 'N Roll tandem, Calfee Dragonfly tandem.
Tandems at the 1976-79 NY International Bike Show
Oroboyz on Flickr has a Gallery of 185 photographs from the New York International Bike Show, circa 1976-80. These include a fair number of tandems. I've culled the tandems from this gallery here. Here's a few examples.
No MKM . . .
But did see a Urago tandem . . . very similar to the LeJeune.
Have ridden some other tandems (lesser known brands) of that era:
Assenmacher, Berry, Borthwick, Bruni, Colin Laing, Counterpoint, Dawes, Follis, Gilmour, Gottfried, GT, Jack Taylor, Kuwahara, Lippy, Montague, Osell, Velo Schauff, among others.