Thanks, 2spot, for the Milwaukee "GP20" (rebuilt GP9) specs (which seem to come from a CMStP&P diagram book)!
There are a number of curious things about it, and I got more curious after comparing to specs for as-built GP9 from the Pennsylvania RR and New York Central RR diagram books (available on-line at George Elwood's marvelous "Fallen Flags" railphoto site,
http://www.rr-fallenflags.org ).
The Milwaukee units are listed as having 645E engines! I'm not going to get burned at the stake defending the truth of that -- clerical errors get made, even in official railroad documents -- but it suggests that they got new crankcases and NOT just new power assemblies on the old 567C base. So does the engine top speed of 900rpm (typical of 645E; the 567C in as-built GP9 did 835 rpm at top speed). So, maybe, do the figures for lube oil and cooling water: 217 gal and 227 gal respectively, as opposed to the 200 gal and 230 gal the PRR thought a GP9 took.
On the electrical side, the Milwaukee units have "D12-B-D-14" generators, whereas the NYC and PRR diagrams just show "D12-B": somebody who knows EMD generators better than I do (not hard!) might comment on whether the "D-14" on the Milwaukee diagram is just a minor subspecification the NYC and PRR diagram peope didn't bother including, or whether it marks a modification.
The Milwaukee units are shown as having D77 traction motors (the model used on EMD's 40-series units): the PRR diagram says D47 and the NYC diagram says D37. (Maybe the NYC diagram represents ealier-production GP9 than the Pennsy ones? Or maybe PRR had upgraded?) But I think many railroads gradually upgraded traction motors on their locomotives.
The D12 generator, unless it was modified and upgraded somehow, does seem like the "odd man out" in this combination!