Your mount looks strong enough but you need to add a plate to it to stop it rotating. The shock puts a diagonal load on the mount and will push it around the mounting bolt that runs through the rubber bush.
Here's a couple of pics of mine. I made mine from heavy walled tubes and they are snug fit over the falcon shock mount.
This pic shows the tab at the bottom that stops the mount rotating outwrads. It's firm up against the suspesion arm.
Tis next show the tab on the inside which stops the mount rotating inwards.
I modified these later to move the moutns for the coil overs inwards. This gave me a bit more clearance for the11" wide rims.
As for welding spatter, buy yourself a can of anti spatter spray. It puts a waxy coating on the parts you are about to weld and the spatter doesn't stick. It's also good for spraying in the tip of your torch to control the spatter buildup in there.
Hope this helps.
Cheers