19s or ES2?

I believe a few of these were made  BUT that is only from Memory.

Yes a 19s. engine. My first Norton was a 55 19s original. Noting the K engine number  It should have a laydown G/box originally but yours not original or factory built. Yours is a Norton and date should be when the frame was made.

Sorry I miss understood your question, though I did read it.(Not enough emphasis on the year. and I've not been well for a while so my apologies, sorry.

My focus was on the 1958 / F / bed 19s. But that will be another debate. ( few I believe were built)

Thanks for the info, Mick.

Frame: 1955, hence date

Engine: 1955 Noting the K in the engine number. (K - 1955) 

Bike is therefore an ES2 with an engine change.

G/box. I don't believe these marched until later Commando's, such as my Mk3. Philip H wrote that these were made in batches and used as required.

Sorry for getting mixed up.

Ride Safely.

Yes, Mick.

Both would have had a laydown box ( Number not an issue) That includes the 350 model 50 if not all road going Norton's. During 1956 the factory moved on to the AMC box. 

I read 55 as 58 initially.....Should have gone to spec  s........

Sorry about the brain fog earlier, but we got there.