I'm trying to assembly some of the ECW depressed center flats for the B&M 5100 series cars.  The trucks that come with the kits are "National C-1" (per the sprue), but looking at photos of the B&M cars:
    https://www.bmrrhs.org/flat_5100_series/#PHOTOS
(in particular at the B&MRRHS Flickr ones) and Richard Hendrickson's "freight car trucks" PDF, they look more like the "Eastern Car Works Commonwealth 90 T" trucks (see p14 - "heavy duty trucks" section of PDF)

Are the old ECW "kits" still the only source for these trucks? (or something else newer now close)?
To me, what is most distinctive is the "reverse arch" on the top of the sideframe (almost all other freight trucks are higher at the springs/bolsters than at the journals, the ones on the B&M cars seem to be higher at the journals than the bolsters)

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Ken Akerboom