You might be thinking about “Pacific HO” out of San Diego they did produce wood cars like you describe that we very close to an SP 1 ½ single sheathed boxcar. My recollection was that you had to decal them yourself.
Paul C. Koehler
I dimly recall that a company advertised in Model Railroader early in the 1970s as selling RTR (no trucks) painted and lettered wood freight cars. Does anyone recall the name of the company and more importantly, if they every produced any such cars? I was in college at the time and could not determine a way that they could make money.
south of Mike Brock