If you look at the dyno cover, at the front, on the engine side, just above the split line in the cases, there's a "bump". On my early sand cast (#260) it's very thin, on my 12/69 diecast (16XXX), like my K1, and probably later K's, it's a lot thicker. You might be able to pick it up in the picture below.
The type font on the valve cover is also thinner on the early cover. The second picture is #260, the lower one the 12/69.
If you have the shifter cover in one hand and a newer one in the other, the old one will feel lighter and the metal edges look thinner. They just feel different, same with the sprocket cover.
I've found subtle differences in the K0 and K1 cases as well.
Hope this helps.
Cliff.