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If it's Campag road double and 8 speed, you'll need 111mm (Record and Chorus switched to 102mm in 1993).
http://www.wiggle.co.uk/tifosi-campagnolo-fit-bottom-bracket/
http://www.wiggle.co.uk/campagnolo-centaur-tapered-bottom-bracket/I think the Veloce has been discontinued, but I'd avoid that anyway as you need a separate tool to install it, whereas the above use the same tool as you remove the cassette with.
PS They are just the first results when I searched: shop around and you might find them a bit cheaper.
Thanks for your reply, my intention is to fit the bike with a double crankset, originally it was fitted with a treble for a touring set up, it was the secondary issues I was afraid of and wondered if there was some kind of formula people used to determine BB lengths, your advice was of some help so thanks for that........