On the fender removal subject, I have had pretty good luck center-punching the spot-welds, and using several sharp/new drill bits while drilling out the spot welds to a diameter a teeny bit larger than a 1/8" aluminum rivet. A hammer and sharp chisel might be req'd to wedge between the fender and batt box to finish the job. After clamping the new batt box to the fenders (plenty of adjustment here to get it right) and installing the rivets, you can prime then paint over them or leave the aluminum heads exposed which IMHO look pretty good. And years down the road, the aluminum rivets are real easy to locate, drill out, and remove for the next (ugh!) battery box replacement.
Home to the 3 splurges - Burly, Scary, Dough (no mo), and the on-going E16 resto.