Ah , we're from the same time zone ! I don't think they would have used a round retainer .. a lot of Japanese bikes used to use a round retaining ring w/a 90 on the end so you could get them off . the best method is a snap ring w/eyes on each end . Anyone that has worked on one of these can chime in and clarify . BTW There is no way that ring can out of the cylinder .
Wellll ,,,,, traditionally / historically , a gudgeon pin is the pin that holds the piston to the connecting rod . AKA , wrist pin . These were press fit , circlip and button retainer that held the pin in the piston .
I'm not sure about this ?
This screen is meant to keep large particles from entering the pump/hydraulic system . These particles , once they get into the system will damage the pump and attack the relief valve and any rotating parts that rely on pressurized oil for lubrication and clearance . If this pick-up is covered and smothers the supply , then you get no oil to the system and everything is destroyed . There are schools of thought that want no screens or similar coverings over the pick-up tube , Me , I like something over it .
When you get this together and bled , pump the brakes a few ( 10) times and see if the brakes release and the wheel rotates freely and effortlessly . If not , see why .