It is a flat-top 55 body style, dark sunburst or black, two "T top" humbuckers, no binding, dot inlays, and a bolt on neck.
With the diminishing quality of US made guitars in the late '70s, both Gibson & Fender were reaching for higher margin products to bolster profits.
The only concrete source to confirm this assertion would have been Gibson's Kalamazoo plant manager Jim Duerloo.
The peculiarity of the TP-6 was seen almost exclusively on tremolo systems (such as Kahler), and was not a popular addition to "hard-tail" guitars of the era adding to the unique qualities of the GK-55.
The GK-55 only came in one color, the two-tone dark sunburst, giving its flat top the appearance of depth, again unlike most of Gibson's mainstream.