Sounds like a nice Skeet 21.
How about a picture?

Someone correct me if I’m wrong.
Diamond checkered forearms were indeed a product of the 50’s.
Serial numbers being indicative of production dates is inconclusive as
Receivers were completed and thrown in a bingo hopper to be drawn out
and used in a random manner.

I believe the Winchester factory coined a new industry term for this procedure.
Oh ya, “Willy Nilly”.