When I drew them up, I seriously doubted the pattern for the crossheads would work. Indeed, I included an extra pair on the drawing in case the first didn’t turn out, at least I could try again.
As it happens, the train spirits were watching out for me, and the patterns nearly worked as designed. A double-fold to give more body to the end where the piston connects failed, but otherwise it folded up just as planned.
To align the piston rods with the bodies of the crossheads, I soldered them in place while the crossheads were still on the fret. The two crossheads held each end of a single .032” rod, which I cut in half before separating the crossheads from the fret.
The main rods are held in place with a sliver of .020” wire, soldered from the back. Again, the train spirits were pulling for me, and I somehow managed to solder the pins in without solidifying the whole assembly. Thank goodness only two are required!