Solved the rear spacing issue, now it looks like this.
I found a proper quill seatpost and added a NOS ITM dual stem... not sure which arm rest and horns I can fit on this tho...
Anyone has a set of Dura Ace 7600 cranks lying around?
Added a brake for proper road testing (Casiraghi Industriale cable for who's wondering):
PS: As I've seen pictures from the 1994 attempt, Moser's bike had as well the fork drilled, but just to mount the computer.