Here is a link to my recent Wevo bar mount & pump relocation
Replacing rear bar mounts 74 911
My friend with the plasma cutter and a bunch of welding experience suggested drilling a hole in the center of the wevo bracket to spread the load.
He further recommended that you not weld the entire perimeter because this could cause the body metal to tear at that point. Better to run a few tacks.
I received some good advice from Grady to First put some sheet metal on the chasis to reinforce the bar mount location. I chose not to do this because i am not going to track my dad's car, well maybe once or twice.
I was also concerned about building multipul layers of metal in that sensitive, highly loaded area. In particular, i was worried about sealing everything up.
We did use "Weld-Through Primer".
HTH,
chris