Greg:
Congratulations on Vitus ownership! It is an unjustly maligned (by some) frameset. Just you remember that Sean Kelly would win field sprints on one just as you have!
I have a pristine one on which I rode and raced many thousands of miles. The pale blue anodized surface still looks great, too. Mine's importer was Mike Fraysee in about 1982-3. Serial number E064604. 120mm will allow a seven speed FW, originally I used a six with the first-ever DA indexing group and then I switched to the seven. Mine came with adaptor pieces to grant me a flat surface for the downtube levers. You should really go to a Stronglight A9 roller bearing HS. Post diameter is 25.0. I have the original engraved Vitus post, and subsequently switched to the weight-weenie post of the day, AmericanClassic. Outside of the Ti Omas BB, the remainder of the bike was pretty much full Mavic, including the yellow, rotational pedals. I personally would never defile a Vitus with SunTour shifters and have left my Shimanos on as they are indeed period correct and original, but I can't tell you how many times I've wanted to purchase old Mavic pieces to fill it out.
The BB cable guide should still be available from Vitus who are very much in business today. You could also try the Nadax Favorit or Edco non-threaded BBs if you think you have a problem there.
Good luck,
Ken, super MTB ride today in fall-colorful MO