I have a Vintage V99 (Les Paul) and I wanted to add a Fender American/Mexican neck to it and I was wondering what changes (If any) I have to make ?

Note: Note sure on the scale length, but i'm guessing it's the same as a normal Les Paul.
Bolt on neck so that isn't an issue.

Help and guidance would be appreciated forum

are you thinking to do it as a bolt-on or as a set neck?
Survivor of:
Maryland Deathfest X
Maryland Deathfest XI
Maryland Deathfest XII
The string spacing is different between the two necks so you'll either notice the strings get close to the edge of the fretboard the farther up the neck you go, or you'll notice the fretboard is too wide the farther up the neck you go. Also there is the problem of the neck pockets not being the same size or shape