A70BBen should advise best as I've never stripped one of these down so far. The overarm has a C-clip holding it and removing this should enable it to be lifted out. I suspect the flipper is similarly held, but watch for possible free-flying springs...
The ball probably came from the horizontal tonearm bearing usually buried in the bearing casting block you haven't removed yet. Can't remember how many balls there are in the horizontal bearing, but there's a C-shaped tonearm bracket which you've removed and at least one ball hidden in this casting is spring loaded, the whole thing held by the screw and threaded top bearing 'spindle' (I apologise for lack of descriptive vocabulary). Have a look at the SL55/65 manual as I think the (shared) tonearm parts are there. It would appear there's a spring and ball acting downwards on the lower bearing 'pin' and the top is screwed down as far as it can go (onto a captive ball?), putting the spring and ball underneath under load. It could be the other way round in actual fact, but it's so long since I stripped one out. It's a crude but pretty effective bearing for the cartridges used in these decks and stayed much the same for the chassis' life I think, getting refinements here and there as the years rolled by. The friction link which grabs the tonearm segment and pulls and pushes it around was the main cause of tonearm friction after the trip assembly is cleaned and serviced (leave the pawls on the cam dry and 'rattly' on reassembly)
*Somewhere* in one of the manuals for this multi-model chassis is a picture of what I'm describing above, but I'm darned if I can remember it
By the way, the platter bearing on early decks had a fibre washer at the bottom. This was replaced by an O ring on later versions, so if the platter has enough clearance, it may be worth locating a 1mm or 1.5mm cross section o ring 'cushion' to replace it. The open end of the ball race usually is downwards I think and is greased, the bearing spindle lubricated with preferably an adhesive oil - modern engine oil is fine I think but I use EP80 gear oil as these bearings aren't the tightest tolerance affairs and the platters usually wobble slightly if rocked.
P.S. Loads here and on the UK vintage radio site about servicing and lubricating these changers, ESPECIALLY the trip pawls on the cam which always seize.
Fun ain't it?