Reading back it seems that Gary replaced the sprocket/sliding member so that ought to have eliminated these? Do a re-assembly without the spring and see if the cam actually allows the sprocket to rotate fully - I don't believe it should unless it's really really badly worn (such as the one photographed earlier) (however if it does rotate fully it's necessary to consider if it still would with the spring in place and fully compressed, which might call for a vice and some measuring).
Incidentally the sprocket in your photo is a 20-tooth which is a bit small for a 500.
5-plate clutch? There's a photo earlier (showing 'cleaned clutch plates') with 6 plates. The concerns about the clutch assembly being a problem relate to whether or not there's a lip at the back of the clutch centre; it there is a lip the back-most plate will be a steel one, if there's no lip it'll need to be a friction plate - unless there is some friction material bonded/riveted to the back of the drum.
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)