I agree with Allen that the preponderance of evidence points to the GE experimental set that later became the UM20C model as being of conventional cab unit form with load-bearing sidewalls rather than being cowl units with all load-bearing done by the underframe. Cowl units were I think quite scarce at the time, and had GE opted for that form of construction, it would have been noteworthy and so likely to have been called out in the literature.
An interesting point is the form of construction that GE used for its shovel-nose cab units. In respect of the initial 1949 design for Argentina (LGB 621 class) it said:
“The platform is fabricated from plates and shapes. It is designed to get the static and buffing loads into the side sheets as near their source as possible. This permits using a minimum section and results in a substantial weight reduction. A housing suitable for A.A.R. draft gear is included at the front end of the platform. The rear end carries a draw-bar pocket and buffer assembly for connection between locomotive units.
“The cab sides and roof are fabricated from sheets and light, bent-up sections. These assemblies substitute for the conventional truss on the standard road Diesel, there¬by saving a large amount of weight.”
(from Railway Age, 1950 November 25, page 37ff)
This appears to have set the pattern for the following shovel-nose variants, and also the Philippines Manila Railroad streamlined cab units and the NSWGR 43 class. I recall reading somewhere that the NSWGR 43 had load-carrying side panels, but cannot retrace it right now. Of the Manila units it was said: “In appearance the ten passenger locomotives from preceding G.E. locomotives through the effect of the fluted side panels, a form of construction which adds to the strength of the sides.” (from Diesel Railway Traction 1956 October page 394ff)
The GE experimentals also had fluted side panels, which might have been used purely for cosmetic purposes but I think which were more likely used for increased strength, suggesting that it had the same form of construction as the concurrent GE export units.
Nevertheless, GE did use the truss form of carbody construction on some locomotives, such as the GN W-1 electrics. Pictures of one of these after its conversion to coal-burning turbine form by the UP (as #80B) clearly shows the truss structure over one section where the body panels have been replaced by mesh.