I have an ACF builders photo (1907) of D&H 27507 - a definite hopper - with "xxxx hopper door service | patented"  on the side.  Very similar construction (at least given the two photos).

Most hoppers and Drop Bottom Gons had some form of patented door/opening/device signage on the car - not unlike that for MCB or other draft gear, brake beams, axles,  and other patented devices.   Were you able to look at the side of this as a new car, you'd likely see the "Hopper" lettering...although most of the time this was in 1" or 2" letters to adhere to the letter of the contracts/license/patent.

On the D&H car, there is even smaller lettering at the top of the non-brake-staff end that can not be determined (using that designation on purpose as the lettering does not appear to refer to the staff,wheel or other brake portions - the New York Brake info is lettered below that though...)



At 10:01 AM 12/29/2019, you wrote:

I found the same listings as Eric, and these cars are present in my 1930 ORER, but not my 1935.

I think they are "legitimate" class HT cars.  There is a clamshell-type hopper chute just in front of the KD air reservoir, and probably a second one hiding behind it.  The design is somewhat reminiscent of the D&H's Seley hoppers in their as-built configuration, absent the steel truss.
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Dave Parker
Swall Meadows, CA

Bob Webber