I'm not keen on welding a washer directly on top of the frame, as I would need to do that for every mount to have the heights identical. That's why the inset square patch you have done appeals to me, as it seems easy to keep all mounts at the stock height that way, with the added benefit that the outer edge of the patch is supported directly by the vertical face of the frame.
Here are pics of mine before I make any cuts. I plan to make patches out of a junk frame.
I have some rust damage on the bottom side as well that I've already cut patches for.
I've attached pics of one side before I weld it in.
