I've never seen Motion covers with different sized resessed slots..
As far as I know the size of the opening in the castings were never changed, and they are all the same size recess... even the small block ones, as well as the new reproductions of them...Both the covers I just posted pics of are identical in dimensions, only the emblems are different. I'd need to see proof that there were different sized openings in those valve covers, I don't believe it.