Finally got around to silver-soldering some steel components of my built-up coupling rods. Only chose this method due to lack of ready access to a milling machine to mill from solid.
Surprised how easy it was once I had sufficient heat. Ended up putting too much solder in some areas as it flashed through the gaps very quickly once melted so I was a bit unsure of whether there was enough to make a solid joint, hence added a bit more 'for good measure'. Turns out I shouldn't have.
Despite all advice about needing absolute cleanliness, managed to solder in solid some temporary spacers made from black mild steel that had only had the mill scale cleaned off with vinegar and were otherwise untouched. Seems like Tenacity flux works pretty well even on dirty steel.
Now to clean up, drill and ream holes for bushes and fit to loco. Will post some photos when they look decent enough.