Well before they were available I had made new bushings for the orignal rods from Oillite bronze as the orignal seemed to be brass anyway. They are available from Cliff and I would get a set as they also incude the upgraded crosshead.
they use the same boiler
I just pulled the Mogul boiler from my #21 and replaced it with a 4-4-0 boiler (already has a sight glass). The 4-4-0 boiler is about 1/4" longer than the Mogul boiler. Also the steam outlet from the throttle (to the lubricator) is on the opposite side. Otherwise they are the same as far as I can tell (besides the sight glass which I already mentioned).