Leaf Spring install

Got the springs and rear end in! Somehow I lost my shock plate nuts and washers. Are they special cupped washers or will a flat one do? I just attached them with a nut and washer I had.

Pic for attention.

View attachment 1715290806

I took some right sized washers , and used a ball peen on a couple of them to dish them to match the stock ones -
Lay the washers on a soft board ''cedar'', and put a ball peen on the washer and strike it w/ another hammer .