Will the Duplo train track extension set 10872 work with Duplo train set 2700?
From a train point of view those wheels will fit happily within the guides of the bridge, and the connections on the tracks should just about fit as well.
I'm fairly sure we bought our bridge when we were staying in a holiday cottage that had a load of the old black track, and it connected to the track successfully, but you may need to work with some curves to find the ideal length as the black ones tend to be slightly longer than the newer grey ones.
LEGO Customer Support have the following to say on compatibility:

DUPLO® train tracks haven’t changed much over the years, so older tracks are fully compatible with the current ones. You can tell old and new tracks apart by the colour: the older ones are black, while the tracks we currently make are grey.
While the different tracks can be used together, we do recommend alternating between them since the older, black tracks have less grip. If you’re building a track with a bridge, we’d suggest using newer rails around the slope.

Their recommendation for using grey around the slope may be aimed at the motorised options so that the train isn't slipping in the build up to the ramp, or skidding at the bottom.