Ufff, I think you may need to have a chat with a BMW dealer and ask if none one here knows the precise answer to that, after all, they sell the bike with the kit installed so they would know how to do the necessary. Good luck.That part is the easy bit. I'm meaning the section that is open where, in your (Anibal) example, the Red side covers are removed and the electrics behind are moved!
Like your lights neat tucked inYesterday I replaced the front wheel of the R18 (original 19er 120 wide) with the spoke wheel of the Classic (original 16er 130). The dimensions at the back remain the same.
In my case, it was actually the case that you only have to swap the wheels at the front and rear. Fenders, axles and adapters are identical.
I am absolutely satisfied with the result. As a bobber she needs balloon tires in my opinion. I'm not a fan of 19 or 21 wheel in the front. But of course it's all a matter of taste.
BMW forgot to homologate the 16 front wheel rims of the Classic for the R18, I have to register that separately for the technical documents. But what about the term hobby: a lot of effort, little return, but happiness.
You can also see the prototype of the Spirit Leather tool roll in front with the Wunderlich tool roll holder. In case of interest, contact them directly (https://www.spirit-leather.de).
A full technical description you can find also in the repair Wiki www.r1800wiki.org