Doubling Down- British Sidecar from mid-50's ?

[fabio]

I posted a request on the "Sidecar" forum to identify and date a Watsonian body & chassis. Brass plaque stamped A4798. I believe it was last\
hitched to a Triumph T140. English current manufacturer a total waste of time....Thanks.

[Rubone]

From what I have seen A=1950, and every year changed up until 72, then started over at A prefix.