Slick 60's

The antenna I have installed has a locating tab. The hole has no notch for that tab. I saw in other antenna posts that the hole is drilled by the installer and it is not a factory stamped hole. So the question is, does this look like the correct antenna, with an incorrectly cut hole? It looks fine aesthetically when installed but the body and base of the antenna clearly don't match.

Not sure about what is exactly right. I've used 55-57 thunderbird antennas because they match the curve and cost less that what the F100 suppliers charge.

I have no proof, but from I remember from way back when, I would guess that is a replacement or later addition to the truck.
I was the guy who painted interiors, added eight tracks, ran additional speakers,and replaced broken antennas in our group.
I would say if it fits the hole and your vision of what it should look like,if it stays put and works as intended you have a winner!
The question I have is do those antennae give you a good FM signal as well as AM? The modern strips that attach to the windshield really suck.

I can't tell you about FM. It worked fine for AM.

The radio doesn't work now and the engine is too loud to hear it if it did work so I want to find a way to plug the hole without welding a filler plate and am thinking about finding another antenna to modify for that purpose.

It is a later addition. I bought the pictured antenna about 17 years ago. I don't remember if an antenna was installed when I got the truck. If one was, it is long gone for comparison. The hole definitely was there.

It looks like that is a correct Ford antenna so I filed the notch. I got a '65-'68 Mustang antenna from Mustangs Unlimited, which is a few miles from my house, made in Taiwan, so it was less than $20 after tax. The mast itself seems the same with a different adapter, bezel, and nut, same thread size. So I cut the wire and mast, got a NOS adapter, bezel and nut off eBay for the truck and made a delete.

If you cut the mast about 1/4" higher than I did, it looks like it is not hollow, so you can finish it a little more nicely.