This one is going to look amazing, omgiv, I love posts like this!
While I am coming to the realization that spending thousands of $, € or whatever on a franken and projects like this generally will need a lot of consideration, a 16520 is on my list also.
I prefer an El Primero franken over the gen actually, 36000 bph and a truly legendary movement beat Rolex's version any day. Thirty something percent of a gen is tough, but the possibility of building one of these with gen everything except the midcase makes it worth it imho! Also the feeling of finding something rare and almost unobtainable and finally installing it in your watch is hard to beat!
Please keep us posted, can't wait to see the finished product!