I'm thinking now that it would be a 1955 frame since 54 and 55 were the only years for a CA7 prefix and this is 13,356, very near changeover to the next frame prefix, FA7. BSA started the CA7 frames at 101in 1954 and were at 7001 by the a beginning of 55, so 7000 frames per year puts 13,356 as a very late 55.
It appears new models start at engine and frame 101 as a rule .
The engine appears to be a 1956 Gold Flash, but why would a Gold Flash be designated HC or high compression? Wasn't high compression limited to the sports models, the RR and SR etc ?
Did the 56 swing arm Gold Flash have an alloy head?
This engine has an alloy head, but it might not be original
Glen