Tony … I produced the SAL B-7 in HO resin and still offer it in S scale.  The HO patterns were sold to Wright Trak Models 8-ish years ago and, I think, are now owned by Greg King at Southbound Model Works.  You can contact Greg by Googling his company name.  The B-7 is the single door version of the AF-1.  Neither car is close to the PRR X31.

Jim King

http://smokymountainmodelworks.com/