Maybe just three “tacks” with your welder would hold them securely.
Might be easier to take the tailpipes off and have them done, or do them off the car.
With most Pantera exhaust systems, there are only the three bolts attaching the tailpipe to the header flange, and then there is the one hanger at the back of the tailpipe.
If you pulled the tailpipe, you would not have to worry about your electronics being damaged by welding, and your welder would tell you if you need more tacks, or he likely could do the whole seam.
If they might be of help, I have two exhaust doughnuts I could send you, depending on your exhaust configuration.
TOP TIP: To get your tail pipes aligned precisely, hang a long straight edge from your bumper with bailing wire. Ensure the straight edge is leveled and aligned with your bumper, and use the straightedge to set the height and rotation of your tail pipes.
There is a lot of adjustment available in the tailpipe hangar, and rotating the tube at the header flange.
Rocky