Thanks to comments from Rob and Richard, I re-examined my approach to the crosshead guide oil cups. Rob encouraged me to look again at the prototype while Richard suggested I think like a jeweller. So, despite my earlier capitulation, I launched back into battle with the oil cups.
It took a few attempts. One was self-inflicted because I forgot to get the cylinder back on before making the crosshead guides too big to fit through the hole. Another oil cup sacrificed itself the moment the soldering iron approached its mate. One was steadfastedly crooked. Fortunately, soldering is forgiving, and I was gaining ground with each volley.
After cessation of hostilities, 622 will have oil cups on the crosshead guides.
At least on one side.