There were reportedly 25K cal 504 movements produced between '57 and '60. I don't know if there are any parts unique to the 504 other than the bridges; 502 and 503 parts should generally be interchangeable. Hopefully one of the technical experts here will chime in if there are parts specific to the 504.
Right off the top of my head I think 35 mm case diameter is correct; if anything, it could be slightly less.
Art