I've emptied the stock box, and taken as many orthographic, or as close as, photos to help. Most are Lima pancake jobs, so I'm not sure what the current Hornby innards are of these. You'll have to google/debate the pro's and con's of each, but most are cut n shuts - never an ideal solution. *When I say "perfect alignment" it does not mean so. The bogies on the A-Class are trimount, and no RTR manufacturer allows for the offset arrangement of the central axel. The central one is shanked to one side.
Deltic chassis as used under the Sulzer - almost right, needs a cosmetic sideframe, and hornby version wouldn't pull hot snot - see Kirley's trials with it on his WB.
Yank thing - SD9? - Easy to cut and shut, no weight, will need cosmetic sideframes, perfect alignment.
Class 50 Hoover - cut and shut job, needs cosmetic sideframes, perfect alignment. Pulling power questionable.
Class 47 - same as above Class 50
Class 31 - Bogie is far too big - sorry Des On the positive, the sideframes are good if you wish to go slightly oversized.
Altas RSD4/5 Chassis - very slightly underscale, but front to back axles are correct, trimount bogie present, no cutting required. Central tank is die cast metal, so unsure how one would deal with it. Warbonnet tells me it's relatively easy to DCC these elderly, but powerful chassis'. I hope that does something to inform this debate. Richie.