Hi mondo, How old is the 2700?
I don't think I'd pay more for an old used model without features that are considered essential on a receiver today.
Tbh unless you have to buy one of these two for some reason I'd widen my options, look and then listen to some other options.
I'm not saying the 763 isn't a very good receiver but if you are thinking well the 763 has the features but the 2700 was, when new, a much more expensive unit so the sound quality should be better then I wait say don't buy either and wait.
The reason being, if you like the Yamaha sound and if you can afford to go upto the £500 mark for the old ex-demo then in a month's time there will be the new 765 out.
This new receiver is pitched between the old 763 and 863 models, it has all the current features and burr brown DACs and other higher end components in common with more expensive units, so it may be a far better option for you than both and dealers are taking pre-orders now for £549 if you could stretch that far. It may become cheaper if Yamaha can do a better job supplying the numbers needed this year.
Hope that's of some use.