Sorting mismatched heads and rockers

[lakeview]

It's been snowing all day so to feel like I got something done other than shovel or blow away the stuff, I looked at my box of orphan heads (for the record marked ZR21, 3217, 1U60 and rockers marked 4F27 and 8U620) and saw that 2 of the heads had an additional set of numbers on the other side appearing to have been stamped when barrels had been installed (B9287 and C2761).
This cannot be that unusual, is it? Any significance?

One of the castings holding the rockers has had the centre boss milled down I am guessing for a one off
clearance solution or is it a special item?

 

[TwoManyXS1Bs]

Best I can figure, from studying forum pics over the years, is that:

Atop the camcover, in the middle, is the bulge for clearancing the cam sprocket. Only the early XS1s were rounded. Everything after that are flat-topped. Here's an early camcover:

And, here's robinc's later flat-topped camcover:

 

[lakeview]

Thank you 2M! I had a vestige of a recollection about the different shape of the early cam cover and your post has clarified it.