I've seen a couple of threads showing front fender replacement. In both of them they stopped short and butt welded the replacement onto the old fender. Is is too difficult to drill out the old one at the door pillar area? Some advice would be appreciated. I'll be doing this this weekend.

Up to you frankly...

Drilling may be more time consuming but, if you're not comfortabe with a butt weld this may be the way for you. It would be considered more "proper" again, if the alternative is a bad seam on a butt weld.

On my -6 restoration we drilled the spots and welded in a new fender. On my current GT project I cut and butt welded in a factory fender with a flare one it.

Good luck.