As I mentioned, I was lucky enough to find this Lionel 4-6-0 carcass that would provide me with several parts for this rebuild, as well as another one in the works (I won't be needing the electronics, in case anybody's interested ):
Practically everything had to be modified, mostly made smaller and less clunky-looking. The engineer's side main rod and valve gear is now mated to the PSC crosshead and cylinder:
A little bit of tweaking had to be done, but it works and actually looks better than I thought (feared) it might! Clever eyes may have noticed that this is one engine that will not be running around in neutral: I attached the radius rod (topmost horizontal rod) to the expansion link not at the pivot point, as with most (all?) 3-rail models, but at the bottom, simulating an engine in full-forward. When it runs the radius rod has a back-and-forth motion, as it should. Very cool to watch and well worth the effort! Now, hopefully, the other side should go a little more quickly...