Galen, I'm not throwing my hat into the ring on this one; but having done a few repaints, it would be helpful if you could mix and match the tenders you have on hand and see which ones will work with the locomotive, then post a list of the ones that worked and the one's that didn't. That will save some time for any potential re-painters, so they can proceed directly to the paintwork; the only issue then, would be matching up any road numbers, special markings, or color schemes with the locomotive. Once your list is posted, others can see if they have any different tenders for addition to the list.
I say this because some tenders will present issues, like bumping into the cab roof when going around curves, and some won't work at all without file-editing, and even then there can be problems. But, these are exceptions; many tenders will indeed play well with other locomotives. The only issues might be pairing an oil tender with a coal fired locomotive, or visa-versa.. then we get into fuel consumption and such. But if we're just going for looks, and it pulls a consist, then we're golden. The only issues then, would be how closely the combination resembles the prototype; for example, brakeman's doghouses, truck configuration, air compressors, all-weather cabs, fireboxes.. that sort of thing.
It would also be helpful if anyone discovers a nice combination, to post a photo (or link) of the prototype, along with an in-game screenshot for comparison.
It all depends on how picky we are, and how much we're willing to overlook. I think it's akin to when an actor portrays a historical figure in a film; sometimes it works, other times not so much.

Cheers!