It's worth nearly the asking price for the cranks and pedals alone. If the Campy BBs are also good, you could probably make back your money on just the cranks, BBs, and pedals.
It would be nice if you could test ride it for a decent distance with your intended stoker. I have owned several old tandems, and each had its own distinct feel. A tandem's feel and comfort are harder to gauge than those of a single bike, and are highly dependent on the chemistry between captain and stoker. Some are like effortless magic, while others make the teamwork break down and turn rides into death marches. I have little idea why, but after 20 miles I'll know, which is why I recommend a good long test ride.
I bet you will be able to make 700c wheels work. I don't understand what all the fuss is about not being able to use 700c wheels on a frame designed for cantilevers with 27" wheels. I've done it on too many bikes to remember, and I've never not been able to! Trek, Univega, Schwinn, Nishiki, Colin Laing, Claud Butler, Panasonic, they all seem to work. I have used MAFAC, Dia Compe, Suntour, Scott/Pedersen, and Shimano brakes. Sometimes you have to adjust or angle the pads quite a bit toward one end of the range, but this seems, if anything, to improve mechanical advantage in my experience. Narrow rims, and rims with non-angled, vertical sidewalls help with the switch. It helps that traditional 27" rims were often quite wide and/or had angled sidewalls.
Let us know how it goes! It looks like a neat find.