Andrew
One book you should get is 'The Squadrons and Units of the FAA by Theo Ballance and Lee Howard (based on initial work done by Ray Sturtivant)
If you had that book you would immediately know that the codes mean the following
ACH: AC = code for 736Sq based at St Merryn and in use between 1943-45 and used by Avenger II, Barracuda II (DN633 was AC-F for instance), Corsair III and Seafire Ib. Letter H was the individual aircraft marking.
AC8: The unit did not use digits, so AC8 is not valid.
I can't help you with any individual aircraft details, since I have no time going through the other Air Britain book you refer to. It is anyway over 20 years old by now and also under serious update for re-publication. A lot more aircraft details has come to light during these past years.
Even if you showed me a photo I would not know if it was taken at St Merryn or somewhere else, but I guess you can make a starting point there....
However if any other codes are visible, I would be happy to help you out.
Cheers
Stig