A possible mechanical modification might have been that the coupler could rotate 360 degrees so the car wouldn't have to be uncoupled at a dumper; I think the PRR put a yellow panel at the car end to indicate that. Only one coupler per car would have to be modified, as long as they kept all the cars facing in the same direction.
Appears to be a standard 2-pocket hopper, altho the pic does not show it too clearly. ORER shows NYC 828787 would have been a 65-ton hopper, overall length 31 feet 6 inches. It shows over 3500 cars in the series so it must have been a fairly standard design.