This is from the retrobike thread about this bike from a very knowledgeable CB individual
"It's clearly not a low end machine, just one that's been dressed up like an 80's Claud. The metal head badge was never produced in those colours so has definitely been repainted in the post 1976 colour scheme. if the silver elements are actually raw aluminium rather than silver paint then the badge at least would be the high end aluminium version used pre 1956.
As for the bike? I need better photos and also a photo of the badge number, 51400 could be 1967 or it could be either 1935 or 45 (5) January (1) production count 400.
Somethings niggling me about those cutaway lugs, just can't put my finger on it.....
@midlife can you ask if it has a straight or arched/curved brake bridge?
Straight would be pre 1956 and post 1976.
Curved would be 1959-1976."
Perhaps the OP could let us know about the rear brake bridge