With respect, while the image is fantasy, and a GB-Nohab equally fantasy, and NoHab I myself have never heard of in any offer to BR or BTC or anyone else in GB, the rest of it has some basis.
GM/EMD did attempt c.1950 to set up a locomotive manufacturing plant in GB for supply of diesel lcoos- both for GB domestic and export. The plant was to have been located near Southampton (AIUI on the site of what became the Ford works) and inconjunction with Crompton Parkinson as the GB EMD licencee. ***
Around the same time, GM did set up licenced loco building arrangements in Belgium (with Anglo-Franco-Belge (AFB) then La Brugeoise et Nivelles (BN)), Germany (with Henschel at Kassel) and Sweden (NOHAB); the Southampton plant would simply have been another one of those.
That is NOT to suggest that Southampton would have turned out anything like a Nohab product, but having said that, all three of the DE SE and BE plants did turn out remarkably similar designs (the nearest Kassel examples being the Egypt AA12), so they might have.
The fantasy upthread images thus are an extrension of one 1950s design into a might-have-been domestic built lookalike, to our loading gauge of course,, and should not be dismissed outright.
The reason this never took off in GB because this was 1950, after the creation of BR but before Modernisation Plan, when BR was fully committed to steam locos and introducing new ('standard') types, and GM saw no market future in it, then, at the time. But it was a serious proposal at the time they started looking into it.
Dismissing possible GM designs due to the GB loading gauge issue and comparing with 'scaling down' matters with D800s and 33/2s is also more fantasy than fact. EMD managed to sucessfully get their GL8 model into the very similar Irish load gauge as CIE 121, and then so on with the JL8/JL12 (141/181). There you have the basis of possible BTC Types 1 & 2 . On the whole, quite a capable manufacturer delivering all sorts of designs to all track and loading gauges all over the world. I am no GM fan at all, I detest the much later 66s, and I don't like EMD engine noise (where EMD stands for Extremely Monotonous Din) even from Roots blown 567s and 645s, and yes I have been hauled by Di3, M61, 52/53/54/55, in different lands, but I do not ever dimsiss their technical capability.
GM did not get as far (AFAIK) as producing loco drawings (well not that I know of). Unless someone knows of some buried in an archive somewhere.
GE (as in GE of USA, not GEC of UK) also submitted plans, although the other way around, locos not factories. In early 1950s they suggested a range of standardised diesels that /more or less but not exactly/ fitted into the original BTC formulated Types A B and C specifications i.e. before this was revised to Types 1 2 3 & 4. But do not appear to have had a factory plan - probably intended working inconjunction with AEI (becasue of historical links with BTH) that bypassed need for commerical licencing.
*** see DIESEL IMPACT ON BRITISH RAIL, R M Tufnell, isbn 0852984383 as one source, and there are other comtemporary references to this