@DrTrainDad, Living near Palm Springs, I'm all about MCM. I've done this type of HO to O scale conversion during the construction of my Palm Springs station.
My station was Mission style. I found an old unbuilt HO kit in the style I wanted on one of the auction sites. I used the included parts and simply doubled the measurements onto foam board. For example a 3" wall length becomes 6" and so on. A steel ruler helps. Easy. This method is easily transferred to any structure from a kit
If you use the Forum search function, type in "Palm Springs Station". I did a pictorial step by step topic on my build process. If you hit a snag feel free to PM me through my Forum profile.
Also, thanks for giving me my next personal project!
John