To fix the connecting rod to the crosshead, thread the headless pin through the front of the crosshead, a paper “washer” wrapped around the rod, the rear of the crosshead (thus trapping the rod in the crosshead), and solder the pin to the rear of the crosshead. Remove the washer after soldering and cut the pin to length. The headed pin fixes the union link to the crosshead drop link in a similar manner – insert the pin from the front. Repeat for the second set, but ensure you end up with a handed pair!
Spare pins are LS92.