Let me bump this, with a plea for hankadam to tell us what he knows... or can find out from his sources.
This is the locomotive proposal referenced in the September 1950 issue of Popular Science (which can now be read courtesy of Google Books). There it indicated (with whatever accuracy Popular Science sources have) that the gasifier locomotive would be 4000hp, and was a project between PRR and "Lima".
Here is where the plot thickens, perhaps interestingly: A considerable amount of research, and key patents, map to General Machinery in Hamilton, OH (which unless I'm mistaken is related to the Hamilton Engine that Lima acquired). For example, the history of patent 2600251, for a free-piston engine starter (an important technical consideration in design for these engines) indicates the filing was Dec 6, 1945, but the patent actually issued, assigned to BLH, in 1952 -- this indicates to me that the concept was still under active development at BLH at that time, albeit perhaps only for ship propulsion. Other patents are 2434280, 2497091, and 2671435. (There are more, but I can't find my notes).
Plot thickens still more. See the paper by Commodore Lisle F. Small on 'free piston gas generator brightens gas turbine future' ... and recall that he joined Lima-Hamilton as Director of Research in 1948.
Can't help but wonder whether this chain of research might have influenced first the acquisition of Hamilton by Lima, and then of Lima by Baldwin. Scott Trostel might have covered this in his historical research of the Baldwin corporation.
The obvious poster child for 'conversion' to a free-piston locomotive is the two-unit GE turbine, conveniently of 4000 rated hp and tested on PRR, that had proven troublesome... largely due to excessive combustion-heat damage to the turbine blading and high net shp consumption by the compressor, both of which are 'solved' by the free-piston gasifier... it would have been comparatively simple imnsho to have installed several gasifiers of appropriate size to align with the existing power-turbine stage (which, iirc, was physically separate from the compressor and combustors in the GE turbine design). Might have been some corporate politics involving this, though, including whether BLW's long-standing relationship with Westinghouse over turbine design would make things difficult...
There is little question about where the problems would come in, though, as we have reports from the ship community about at least one big problem -- noise. In an ASME paper from 1954, McMullen indicated "air intake pulsations could cause unpleasant conditions in the engine room if the dimensions of the space were such as to produce resonant conditions within the operating speed range". These were S.I.G.M.A. GS-34 gasifiers, and tource of the noise reported was the INTAKE ducting to the gasifiers, which was light steel. Similar issues were reported for the gasifier plant applied to the SS William Patelson in the Liberty Ship Engine Conversion Project, where the issue of 'high pulsations in the engine room' were only addressed with 'high repair and redesign costs', and the gasifiers were derated from 1000 to 800 nominal hp each.
I for one will be VERY interested to hear a Rentschlerian version of this project...