WZ877 - as a self-confessed Chipmunk pedant, a few more thoughts.
1. In 1973 your aircraft just may have had the scheme depicted on "J". The scheme was introduced by H.307 in 1973, but as aircraft were only repainted when their condition required it, it may not have carried this scheme in that year. It's really hard to tell the two schemes apart in most B&W photos - the wingroots are the clue.
2. I'm not sure, but I read this as you wanting to paint the aircraft as it was in 1973? Bear in mind that the stencils changed throughout the aircraft's life (e.g. the NATO "hook" lifting point symbol didn't appear until much later), I'm still trying to pin down a date for the halved black/white spinner and the white striped blades (certainly not in 1973) and all Chipmunks carried underwing serials until at least 1983.
3. Assuming your Chipmunk is currently in its RAF markings, photograph/measure all markings before it's stripped. I'm always amazed at restorations that fail to replicate markings accurately - incorrectly styled serials are a common error.
Hope this helps!