Those bearing circlips are a nightmare so I bought the type with the little loops on each end. My bearing supplier managed to find some with the correct thickness which I think were from USA.
AFAIK the only difference between early & late cases was the strengthening plate for the cams
And the placement
Early cases had the cams closer together and the cases end to crack around them'
Am yet to see a clean one
They cured this by widening the space between the cams wih a bigger pinion and of course he carrier plate.
Not sure when they did it
The M23 is the early narrow case .