The wheelbase on the inner 3 axles of each truck is 6'8-1/2"+6'8-1/2". The EMD SD9 and successor 6-axle machines have 6'9-1/2"+6'9-1/2", and both Aristo and USAt make versions of that truck, with the motorblock available as spares, if you can live with the 2" scale inaccuracy over those three axles (about 70thou total) and the wrong size wheels (or change them, probably easier on the aristo unit than the USAt, but the USAt is cheaper and will go round tighter corners).
That'd give you a 2-1C+C1-2 with 6 out of the 8 prototype axles. If you wanted more grunt, the 4 wheeler truck from the USA 44tonner is 6'10" wheelbase, just like the original's pilot truck, though it might be difficult to get it to articulate under the pilot deck on model curves. Then you'd have an unprototypical B-1C+C1-B, but it should walk away with most things you could hang behind it...
Or you could buy four aristo porter 2-4-2ST's and gut the mechs to get 8 single axle drives (these wheels would be slightly oversize). Anyway that you skin the thing you're up for custom sideframes, particularly as at the outer end they turn into the pilot deck, but it doesn't look like the detail there is totally impossible - I'd make one good axlebox and resin cast it to get duplicates for the model rather than sweat to make 16 identical parts.
J.
