The Norton booklet sez they made 5550 bikes in 1946, commencing with 1001.
They would be 16H and Model 18, no idea of the mix, don't think there were any Big4's that year.
There were of course quite a number of civilianized 16H coming onto the market,
and the magazines of that era were full of all manner of parts for them, ex-WD,
engines in crates for a few quid, pistons carbs magnetos, etc etc etc.
Do you know the history of your bike ?