The loom will wire into the Nova, yes. I don't really know much about the 1.6 16v conversion wiring, but if the 2.0 is anything to go by, you won't need to take out the dash. The wires should be spliced under the bonnet somewhere.
The conversion should be relatively straight forward for you seeing as it's a 1.6 8v your fitting the 16v to. Fuel system is ready to go (high pressure pump/lines already there), you can use the Nova's gearbox, driveshafts, etc and the engine will sit fine on the Nova mounts. The wiring will probably be the hardest part of the job