Rod,
1) Since parts for the Marelli are now NLA, I'd suggest locating a Bosch unit and have that recurved for your application. Displacement, cams, compression, and gasolines all must be factored during that process.
2) The 2.7 distributor from the '75S doesn't fit the early (2.0-2.2) cases unless its machined down to 27mm. Thats a job for a pro.
3) You don't need vacuum advance unless you require maximum fuel economy,...
Initial and centrifugal will get the job done.
4) Without knowing anything about your engine and precisely what was done, all one can do is speculate. Leakdown testing shows when the rings have seated. Unless you do this on an engine dyno, it takes a few thousand miles to occur in the car and that really depends on technique.
5) Richness depends on carburetor jetting, fuel pressure, and float levels. You may need to make some adjustments.