I'd have to say that the Chehalis Western #684 would be the closest to Portland, Oregon. This 415 was built on Hi-Ad trucks and is currently on Tacoma Rail and is reportedly on lease to American Orient Express. They are leasing the ex CEECO shop for repair of their coaches and use the engine as a shop switcher.
I had also heard that the Alco V-8 251 had been replaced by a Caterpillar engine. This is RUMOR, I have no proof, though would like verification on it.
Pat Connors
Buffalo Southern RR