Total and utter fantasy time....
As you know, a group in Great Britain has been building, from scratch, a new Pacific-type steam locomotive, to the (very slightly modernized) design of a late-1940s class that is otherwise now extinct.
So, suppose a whole lot of American railfans put up a whole lot of money... And assume that enough Alco archives got saved (didn't a lot of papers go to the library at Union College in Schenectady?) to provide plans. Could we now RECREATE a Dl-109, which could then (in different paint schemes) be rented out to pull excursion trains in various parts of the country? It wouldn't (like the project of recreating the Woolly Mammoth) need advances in basic science: that's the good news. Would it be feasible?
Assume-- this amounts to about maybe about half of cost of a new diesel-electric locomotive-- that someone is willing to sacrifice a couple of S-4 switchers to provide the engine/generator sets. (If we don't assume this, the project gets much bigger, or, if we start thinking about hypothetical re-engined Dl-109, less well defined.)
----Doyle McCormack had to use trucks from a Fairbanks-Morse "Erie Built" in restoring his PA. At a guess this means that getting the truck frames cast for an accurate restoration was beyond his budget. At a further guess, truck frames may be the biggest hassle in re-creating a Dl-109 (recall that the Dl-109's trucks weren't identical to either the PA's or the Erie-Built's). Recent GE locomotives have had trucks with frames cast in South Africa, so expect to source ours from outside the U.S.
----The GE 730 traction motors most purchasers specified for their Dl-100-series locomotives are almost certainly not available, but the New Haven's units had GE 726 motors. There may be a few 726 still around in non-rail applications (a couple of years back I came accross the WWWeb site of a company that advertised replacement parts for GE 726 motors!), but even better: I think the 726 is dimensionally interchangeable with (at least early) GE 752 motors.
----Complete authenticity in smaller, less visible, parts is probably not to be hoped for. In some ways this may be just as well: do you really want wiring with 1940's-style insulation if better, modern, materials are available? Probably a fair number of small components that Alco got from outside subcontractors are now out of production. And if we use heftier 752 traction motors there might (I don't know; I'm not an engineer) be a need for some redesign of the electrical system to mate with them. If it would mean I could see an operating "Dl-111" I'd be willing to make these compromises.
----So I think it would be a big and expensive, but not impossible, project. Certainly a lot easier than recreating a modern U.S. steam locomotive: whatever grief you'd have getting Dl-109 truck frames cast is NOTHING to what you'd go through getting a one-piece cast engine bed!
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And when it comes to "non-prototypical" color schemes... One of my favorite "alternative history" scenarios involves the Massachusetts government and congressional delegation getting, in the early or mid 1940s, a subsidy arrangement to upgrade "Inland Route" (NYC to Boston via Hartford, Springfield and Worcester) that financed some Dl-109, built to New Haven specifications, for the Boston & Albany to institute run-through operation... units which, in the 1950s, would be repainted in full New York Central lightening stripes.
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O.K., I'll go lie down. And take my pills.
