That's great news Phill
... and you're taking the right approach by commiting to a full rebuild at a leisurely pace since your Nova's already on the road.
As for the noise, it sounds more like a top end rattle (especially when the engine is reved a bit) rather than the heavier knocking sound of the bottom end. However, if it was the top end I'd expect the engine to be running rougher.
It's difficult to make out from the video if it's smoke or condensation coming from the exhaust. Anyway, given that you're planning a full rebuild you should be able to find out what's wrong and put it right.
Really looking forward to following your rebuild
Alistair