How I spent my day - "Home-Brewed" a Stainless Steel Valley Tray

Looks nice.
Did you use adhesive kit to glue them to the heads?
I suspect you'll still need to put some strengthening ribs in the plates to prevent them from deforming over time...

The Indy valley coverplate used with INDY heads is a cast plate of some 3/8"(?) thick aluminium.
I'm sure it would be thinner if they could get away with it.

Did you use nuts and bolts to secure them together in the center?
Or just bolts in threaded holes?