Need help removing inner fender

[70 shorty]

I'm trying to remove the inner fender to get to the heater core. Natually, I've got the hood off, and all the bolt except for the last 2 on the inner fender. They are as you're looking at it, the bottom and next to the bottom one on the backside of the wheelwell, that attach also to the fender lip. Apparently, there must it looks like a nut on the backside is just spinning. I've shot them with PB Blaster, as best I could. I was trying to get them off with an air ratchet, then tried a hand ratchet thinking if I took it slow, that might work, and obviously no luck. Any Ideas? I can't see anyway to get a wrench on the nut to keep it from spinning.