Hi Chas,
I like your approach. Here are a few suggestions: a green Penn Central box car, a TOFC from any eastern road, a Canadian National box, A Canadian Pacific "Pac-Man box (newsprint from Canada), a N&W box (a nod to the Dereco mother ship), an N&W or B&O hopper of soft coal (most northern industrial boilers ran on soft coal), an EL open or cylindrical hopper or box car, a Santa Fe covered hopper, a New York Central box, a yellow D&H box or a red or grey covered hopper, an Erie or DLW gondola (some were still in old paint), maybe even an N&W caboose! A former Erie repainted EL bay window caboose would be most common, especially in the west where the E8 were more common on freights (Me? I'd have a EL painted Dunmore or Keyser hack).
How about a high and wide load (but not too big in a regular consist)?
Look into any of the many colorful Morning Sun Books featuring the EL.
Are you modelling the west end or the east end? The consists vary on either side of Meadville or even Binghamton.
I like to create EL power consists too, especially with a mix of different models of EMD, Alco and even FM power. I like to elicit reactions to my mix from visitors to our club layout. It always starts a nice conversation.
Have fun!
Earl