Those cars all work together. The ones with the black hoods are called "box couplers" They were introduced in 1935.
You can date the three cars in the picture below by trim:
- brass to mid 1934 on hopper
- mixed brass and nickel mid 1934 into 1935 on tank
- all nickel from mid 1935 on boxcar.
You can also date those cars by the trucks:
- Hopper has the rectangle type truck used until late 1932, with maybe a few leftovers in the 1933 model year.
- Tank car has the two triangle cut outs (usually called ex-IVES truck) with copper journals which dates to 1933/34
- The boxcar with the two triangle truck with tang for box coupler (can't see it in photo) and nickel journals from very late 1934 early 1935.
Those boxcar and tanker might have even come in a set together. The hopper is too early to have come with the other two cars.
