Should be no problem using your rubber if its a new one. I have heard that it is much easier the get a 'screen in there with a genuine rubber due to a better fit, but by the sounds of it yours would be genuine.
I had a bad experience having my screen replaced under insurance. I supplied a genuine rubber myself and one of Australia's biggest windscreen fitters put it in...... but I think they sent the apprentice! After much swearing etc. I went out to see him finishing the job only to see him using a screwdriver to push in the anodised trim after [/b]it was in! With numerous marks around the edge of it he said "She'll be right mate - use a bit of sandpaper on it" (you have to read that in an Australian accent!) I spent many hours removing the screen, getting the trims reanodised, which they stuffed up, then repolishing myself to have them done again to a passable quality and refitting myself which was really quite easy. Eventually after much arguing I got the company to pay for half the cost of new trims but boy what an effort.
So the big advice from me is get a recommended windscreen fitter and not just a company name, an actual persons name. I know of a good one in Adelaide but that's a long way away!
'69 280sl