No, Monongahela's weirdness was BLW "Sharknoses." EDM5970's suggestion is plausible: that the railwelding cars (as the units had become) were serviced on the BLE at some point, explaining the stencil. I have no information of when the ex-Erie-builts were used in railwelding service. I recall seeing what must have been one of them, on a siding near the Albany-Renselaer Amtrak station, in (probably) 1976 or 1977. Painted a shade of blue not too far from Conrail's locomotive color.
I asked the right guy the right questions today, and found out that the trucks were from PRR B units. My source thought they were used in rail grinding service, BTW.
The units (4 in all) were used in the east, and wound up in storage in Smith's Falls, Ontario, before moving to Western Canada. Three units were scrapped, but the fourth is still around, in Canada, and may still be relatively complete.
In spite of being on A-1-A trucks, PRR used these units as freight power, and they were painted and geared as PRR freight power.
Doyle got the trucks from the scrapped units; one pair is under 190, one pair is under the Smithsonian's unit, and the third pair is being held as a spare.