Hey Damien,
I agree with Jim. Just clean it up with a mild detergent and when it's dry, apply some liquid wax it to keep it from rusting any further, replace tires, the bar tape, brake cables, housings and hoods, lube it and go ride. Okay, I'd replace the SunTour shifters too. And guess what? I have a nice Campagnolo Gran Sport rear derailleur that I got a couple of years ago from Mike Frayse. The project I had in mind never developed, so I'll be happy to sell it to you. I don't remember what I paid for it and I don't have any idea what it's worth. If you can come up with a fair price (maybe with a little help form our friends) I'll send it off to you.
Mark
Mark Fulton Redwood City California USA
PS: I wouldn't worry about the mismatched Weinmann calipers. When I bought my 1950 Dutch-made Locomotief Tour de France in 1960 it had a Type 500 in the front and a Type 930 in the back. Still does. Still stops and looks great.