Just a note to add to this, some information provided by both KP and Steve Swan on the diamond waffle cover.
It seems a few known covers which have cropped up all have a weld to the end of the tacho cable screw boss. It could possibly be a preventative measure to add more material to the area prior to boring/machining the thread, as opposed to a repair after cutting the thread.
Note also that the sandcast rocker covers have a thinner lip where the breather hose exits the rear of the cover, and I believe this continued to the end of the K0's.
I have posted pics also of the 'type 3' rocker cover, dated 30 April 69. So this last sandcast / early diecast version came into production very quickly. I have noted a 'type 2' rocker cover on a 55xx sandcast too, so as per the tokico calipers, you can get an early rocker cover on a later bike, but unlikely a later cover on an early bike, unless swapped out.