FC Rear Sway Bar Mounts

I decided last night to throw the ST rear sway bar on the RX7, since it's understeered piggishly at the past two weekends events and I have another auto x coming up this weekend, figuring it would be a causal 1 hour job. Put the impact on the first bolt on the drivers side mount and immediately broke the captive nut loose. berkeley! Miraculously, through much abuse with the impact, I managed to get the bolt out and think I spared the rest of the nuts (wisely skipped the impact), but now I need to get in and weld another nut in place. 

Best thing I can figure is cutting a window through the driver's side rear wheel well, but I figured I would see if any of our FC gurus had a better idea before I go putting holes in the car. Also, should I be sketched out weliding that close to the gas tank? Rather not blow myself up.

I don't run a sway bar so I don't have any good advice but if I were you I would drill 4 holes and then connect them by cutting them into a square/rectangle shape then re make the part with a new captive nut and weld it back into place.

I've welded much closer to the tank you should be fine. (gas tank skidplate)

Well, as luck would have it, I decided to just try tightening the damn plate down last night before cutting holes in anything and it worked. Don't know if I somehow jammed the captive nut against something in the process of rapidly going forward-reverse-forward-reverse with the impact to get the old bolt out, or perhaps I just jumped to conclusions. I'd feel like an idiot if I weren't so relieved