The largest was a V-12, which was used in three applications; one engine was used in a single-engine steeple-cab locomotive, while two of them were used in the large road switcher that Westinghouse built in the mid-1930's. This engine was as mentioned 9 x 12 inch, four stroke, and normally aspirated.
This photo, from an old and uncopyrighted volume in our collection, is the engine in question. Viewed from the auxiliary or pump end, we can see one of the two sets of ganged fuel pumps (six units here; six units on the opposite side of the engine) as well as the two water pumps. A railway style generator and end-mounted auxiliary generator are just visible. Note that the cylinder head design provides for intake on the outboard sides of the engine cylinder banks; here, a unit intake manifold is seen with air filters mounted at each end. Two exhaust manifolds are visible, one for the forward six cylinders and one for the rear; this matches well with pictures of the CGW center or "steeple" cab unit before repowering. This engine was rated 800 brake horsepower.Much more interesting is the next photo.
This photo shows what appears to be an identical engine; however, immediately visible is a supercharger mounted above the generator. The intake manifold arrangement has been altered to accomodate feed from this two-rotor, very likely gear-driven blower. An earlier shot in the book labels a very similar looking blower as being a Connell Supercharger; it's unclear if this is that make or not. What is clear is that we've never read of a supercharged Westinghouse V-12 before. Westinghouse did build one unit with a supercharged inline 6, which raised the rating of the six-cylinder engine from 400 BHP to 530 BHP. If that correlates well, then the engine shown here would have been capable of over 1000 BHP. No data are given in this book- just two cryptically labeled photos. Interesting indeed!Perhaps as interesting is the clear evidence that Westinghouse was using an extended engine bedplate to support, and thus align, the main generator. Had this knowledge been transferred from Westinghouse to Baldwin, the latter might have saved itself numerous headaches, in terms of engine failures in the field and warranty coverage.
Certainly it looks like a gear driven blower -- comparable to the Roots blower on non-turbo EMD engines -- in the photo. Kirkland discusses the supercharged Inline 6 in his "Dawn of the Diesel Era," p. 126: the text speaks of it as "supercharged," but the caption on a photo (unfortunately showing the engine from the wrong end, so not providing a very good view of the blower) says "turbocharged": I suspect the photo caption (which may not be Kirkland's: I think picture captions often get put in after the author has turned over the manuscript to the production people) may be in error.
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Your 1060 hp power estimate for the supercharged V-12 is in line with locomotive diesel engine power evolution: according to Kirkland, the locomotive with the supercharged straight 6 was delivered in 1937, so that is a likely date for experiments with the supercharged V-12. (It wouldn't have been much later: Westinghouse stopped making diesel locomotives after that, going into partnership with BLW instead.) Alco seems to have started out planning its 12-241, with 7/8 the cylinder displacement (10.5" stroke instead of 12") but running at 10/9 the speed (1000 rpm instead of 900 rpm) as a 1000 hp engine, only going for 1500 hp at a later date when its GE partners came to them and said "We build turbochargers for AIRPLANES; how hard can it be to design one for a locomotive?"
Other factoids from the Kirkland book. Westinghouse only started building its 9" by 12" version of the Beardmore engine in 1930: the first few Westinghouse diesel locomotives were powered by 8.25" by 12" engines imported from Scotland (but given Westinghouse badges before installation). ... There WAS a bigger engine: the two 2D1 units built by Westinghouse and CLC for Canadian National in 1928 had Beardmore-built V-12 engines of 12" bore and 12" stroke (so: 178% of the displacement!). Kirkland says that one of these engines was tested, on a test stand, with a supercharger, though they were never operated in the locomotives with supercharger.
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Modifying diesel engine designs with different cylinder dimensions seems to have been a less traumatic business in the 1920s and 1930s than it is now: W-house slightly enlarged the "small" Beardmore at a time when Beardmore themselves also had a "large" engine, and Ingersoll-Rand also had two sizes of engine: nothing like the multi-million dollar investment and "50 locomotive years" of prototype operation before GE replaced the 16-FDL with the GEVO! I suppose the lower power, and so lower stress, in the old days may have made the engineering problem easier?