How did the PRR tend to run these? A-B? A-A? A-B-B? A-B-A? Some other combo?
@Andrew B. Just went through my Staufer books and it seems all configurations were used. Several photos show ABA, but also AA and a few AB. There is an photo of an AAA, but it is an F3/E-B/C-Liner combo. There were 36 A-units and only 12 B-units, so with the 12 extra A-units I imagine AA combos were common. Keep in mind the Erie-Builts were 2000hp vs the F3 and Shark with 1,500hp, which may be another reason why there are several photos of them as AA.
The Pennsy initially bought a combination of freight and passenger Erie-Builts (FF20 and FP20) , then shortly after that regeared some of the freights to passenger (FP20a). They didn't do well in passenger service and all were converted to freight (FF20). I have not been able to find the date when the Erie-Builts were all converted/regeared to freight.
By the way, FM's 10-cylinder opposed-piston engines were great in submarines but did not transition well to land. They were initially not reliable and by the time FM worked out the bugs with the engine, EMD had taken over the market. FM could not get a foot hold, and like Baldwin and ALCO, soon left the market.