I have a pair of frame stiffener panels that appears to be made by Restoration Designs.
One appears to be an older version as it is bare steel while the other is primered.
The RD part numbers are P346 L and P346R.

https://www.restoration-design.com/store/product/PP346L
https://www.restoration-design.com/store/product/PP346R
The older one is a single piece whil the newer one it in two pieces.
The non-primered one has light rust. I can have it sand blasted at cost if needed.

Offering these as a pair for $300 compared to the retail of $440.
I can ship from 92505 or local pickup.