Originally Posted by
El Chaba
The existing P3 likely has a crown race diameter of 26.5 mmm or possibly 27.0….A Campagnolo will have a 26.4 mm crown race which will require machining with a proper cutter.
Very tricky holding the crown race in a lathe chuck, and probably better to grind it as it is chrome-plated.
Almost certainly better to re-do the fork seat.