Btw, when you say "component modification" do you mean that you altered the headset to reduce its stack height (which was really my first hope; my question to the LBS was in fact "Is there anything I can do to this headset to reduce its stack height?"), or simply went with an alternate headset?
I decided to go with the original(???) head set, because I like the looks and it was in great shape, but the steering stem was too short to allow for this set-up...
The center pull brakes caused two problems. The bracket was too thick, increasing stack height and, the leverage applied through using the brakes would loosen the lock nut off in short order.
I am going with Universal 68 side pulls, and I swapped out the brake bracket for the thinnest spacer washer I could find in my stash. Then, I got rid of the cages/balls and went with smaller ball bearings, but more of them. The result looks like it should be OK and the Bottecchia sits, waiting for some decently dry roads to test the bike, and the modification, on. My guess is that the fix will be just fine since I have a decent thread count now.
I can still, if I wish, grind off some of the bottom of the lower cone, gaining another mm, with luck. But I doubt that I will have to.
Hope this is a help and that my fix worked. Don't even ask about the Bottecchia Special that I am also interested in restoring.