In my excursions in to modifying motorcycles I have always had fun building what "could have been." I built a dirt bike out of a 1973 Honda XL 250 motor, bored and stroked to 360cc in a 1984 Honda CR 500 frame. Nothing on the bike was not available in 1984. I finished it in 1996 the same year Honda came out with their XR400 and mine would blow it's doors off! It is still running and because of the long swing arm it is a great hill climber.
Jim has built an engine that "could have been" built back in the '70s but wasn't. The technology was all there (except for maybe his crank firing electronic ignition) but nobody did it. The look will be the same. My gut tells me the durability will be through the roof, and the power should be rather "other worldly" in the Norton world.
I also like to think that the Norton "heavy twin" platform had more potential for this kind of extreme upgrade than most other engines of the day. I'm talking about keeping it all in almost the same size package rather than just taking a design and making it bigger in its outside dimensions. In other words, it will still look like a Norton Commando engine and not just a much bigger engine which just copies the original look.
Dan.