Can I replace the inner front fenders on my '71 Chevelle by just jacking up the car, taking off the front wheels, and sliding the fenders out that way? Or do I need to take off the whole outside fender too? I haven't look that closely at where they are all bolted on, and if I can even reach all of the bolts. Any suggestions?

No need to remove the fender.

After the car is on stands (under the frame) remove the tire/wheel and all the bolts for the inner fender. The rear of the inner will drop down, then 'roll' it out over the hub. On the pass side, you'll also need to remove the battery and tray.