Viktor (above) got this Model 18 from his very good friend Vratislav (below, on the right) but it took him 10 years to persuade his friend to part with the Norton's remains! He had to help him out reproducing quite a few parts for Vratislav's other bikes before he could carry the Norton project home.
Viktor has now dismantled the engine and surprisingly, it looks in quite good shape still. The head is marked 29-1-27 and the engine number is 35036 which confirms 1927.
Rebuilding the frame will be the biggest challenge but Viktor is making progress, see this earlier blog entry
for more info.