I've only seen pics, but unless the fretless fb was a bit thicker than the fretted fb, string height would need lowering for the fretless neck. I saw one for sale on eBay years ago. Not sure what neck-pocket it fit. And yes, they would sound different - one fretless and the other fretted. (if that's what you were referring to)
I meant more if the FB was "fastened" to the neck instead of glued on...
My initial thought is if the neck was reinforced and bone straight, you could have a carbon fiber sleeve to slide the FB in an out of and have locking mechanisms on the low string side (not much traffic on that side) or have it slide up and under the strings from the neck heal and again have CF guides on the sides (could look almost like neck binding)
I imagine you'll lose some tone/sustain though...


