David,
The mod needed at the cam chain sprocket is to retain balance of the camshaft assembly, the flange with the pinch clamp is quite a bit heavier on one side. As Marnix has stated, it works very well and is easy to fit. The hole in the sprocket won't weaken it enough to create any issues.
Marnix' rockers are stock late type, commonly referred to as "SFC" type, but were fitted to at least SF3 models, if not late SF2s also. Looks like they have a stellite or similar plate brazed to them for the follower face, also a common repair/reclaimation bodge process. In reality, probably a lot more durable and accurate than a stock rocker!
piet