My '69 EB has the long tapered dash knobs instead of the short round flat-faced ones. About 3 of mine were missing the concave center. I wasn't sure if they could be removed or how much trouble they'd be if they could. I was doing some dash refurb & really wanted the centers in them. I took some spackling & packed it into the opening. I then took a 1/4" stainless carriage bolt, (Stainless 'cause the head was smooth & 1/4" 'cause the head seems to be the perfect size & shape.) & wet the head in water & pressed it in Anyway, it pressed the excess out & I packed in some more & repeated. Keep the head wet & use a twisting motion as you press & remove. Repeat until it looks right. Wipe off the excess & let it dry. Clean it up with a damp rag & fill in any blemishes using the bolt head again. finally, after it's dry again, clean it up with some fine sandpaper or maybe a Scotchbrite pad, tho I used the sandpaper. Seal it off with some super glue & a brush or any other clear sealer of choice. My restored ones are a bit whiter than the others, but they all could be touched with a dab of paint to make them all match. Anyway, I think my 3 restored ones look real fine, definitely better than no centers at all. I thought I'd post this in case anyone else could try it.