Not sure where you'd get a vintage Vitus hanger, but my old Giant used to use a front mech hanger similar to the one shown above. Looking at the position of the threads on the frame the angle will be wrong I'd say. Looks like you need one like this.
Hi, thanks so much for your reply, some really helpful links there, just need to work out which hanger will be compatible with my frame or put up with a band on mech or mech hanger...
Not sure where you'd get a vintage Vitus hanger, but my old Giant used to use a front mech hanger similar to the one shown above. Looking at the position of the threads on the frame the angle will be wrong I'd say. Looks like you need one like this.
Giant appear to do quite a few different shapes/styles: http://www.moruyabicycles.com.au/contents/en-uk/d87_front-derailleur.html
http://www.jejamescycles.co.uk/giant-front-mech-bracket-id42767.html