The tanline on the neck from the other body:
This is pretty common when changing necks. Although theoretically the bodies should be the same, there's almost always a small difference.
Some of it can be attributed to age and different properties of wood, shrinkage*, etc. And some of it has to do with the way the neck was shimmed in the pocket. Do you have a shim in there?
I always try to rub off the line with rubbing compound and then polish the area. It can usually be minimized if not removed entirely.
Your JM looks GREAT!
*
I WAS IN THE POOL!

Q. Are we not men?