Picture 2- chop about an inch or so above where the lowest branch is coming off on the right- that can be your new leader. Chop straight across an inch above to allow for die back without killing that branch, wait for buds to develop and grow off the opposite side of the branch, and once they harden off, pick a strong one somewhere on the opposite side, but a little lower than the base of your new leader and cut at an angle from the base of your new leader to the base of the branch you chose on the opposite side. This will give you some nice movement, a smooth transition, branch placement on the outside of the curves and two branches right at the edge of the large scar which should help to heal it quickly.
Just my opinion obviously. I have used this method once or twice and am in the first phase of it with a new tree right now- sometime during this growing season I will finish carving out the angled cut.
I have tried to do the angle cut initially without first developing a bud on the opposite side before, and while it might work fine, chances are you won't get a good bud to pop where you want it in the opposite side of the main leader, the wound won't heal as fast, and you won't wind up with the best branch placement. You seem to have a decent branch there to use for the new leader- puts you 1 step ahead vs a tree that doesn't have good low branches!
Now, obviously, I am only looking at a 2D image, the branch I would select for your new leader may not be at as good of an angle as It appears to be in the image, maybe in 3D the branch has a funky scar or issue there that you don't like- ultimately it is all up to you of course, but that one looks like a slam dunk decision for me!
Now, take into account a few things first- how long has the layer been separated from the parent tree? If less than 2 years or so you probably want to just let the thing grow and gain some vigor this year! If it has been a long time since separation, but you hacked the roots up pretty good when you planted it - same thing- let it grow for a while... This variety of Maple is not as wimpy as a lace leaf might be, but probably not quite as vigorous as a Trident or a regular old Green leaf Japanese Maple and you might want to keep that in mind when deciding when to make the cut.... I am sure Bryan has given you all the info you need to make a wise decision though. If this thing is healthy, well established and ready to work on- have you considered air layering the top off it? As you stated, not an easy variety to find around here, might be cool to have an extra one right?