Don't have it welded on the car.

Even with the ground clamp as close to the weld as possible I wouldn't take any chances of having an arc finding its' way through your bearings or anything else with close tolerances.

It's just bolts to get it out of there and on a welding table where you can see what you are doing and it can be cleaned/prepped properly. Since it's a weld that failed it's all going to have to be v'd out and done right. An experienced welder should be able to do this for probably 50 to 100 dollars. Something to keep that in mind vs the cost of just buying a new pan.