The inner aprons are welded in. Drill out the spots and weld the new panels in. This is also an excellent time to inspect for rust, make sure you check everything.
Replacement inner fenders are relatively inexpensive, but make sure you ask what you are ordering before you order. Scott Drake's (battery side) front replacement is a good heavy gauge piece whereas the driver's side is a little weak and has no cutouts for fender bolts. Just be sure you know what you are ordering.
http://my67heven.tripod.com/emsm.gifI was looking for a restoration of fantasy. I do not want my car to be as it was in 1967. I want it to be as I imagined it in 1967. -John Baird Got Rust? 1967 A-Code Coupe