Here is some information to confirm what I guessed at about Z4642 and Z7903. The following two sections are from the book "Fleet Air Arm Aircraft from 1939 to 1945" by Ray Sturtivant, I.S.O. and Mick Burrow. This book is a 480 page listing of all the serial numbers of every aircraft in the Fleet Air Arm and their dispositions during their careers.
This confirms that Cork flew two aircraft during the operation. Z4642 in the morning for the majority of his claims on 12 August and Z7093 for his last claim that evening. This would fit with the fact that Cork had to expend the majority of his ammunition on his last kill of the day. If Z7903 was a Mk.Ib with .303's then they would not have had the hitting power of Z4642's 20mm cannon. It would also explain why he as able to shoot down more aircraft in the early engagements of the day. In fact "Britian's Fleet Air Arm of World War II" by Ron Mackay states the reason for R.J. Cork's success was because of the cannon armament of the Mk.Ic which would agree with Glider's statement in his last post.
This leaves us with the codes on these aircraft. I believe that Cork's chosen aircraft would have been Z4642 because of its armament. Most books seem to focus on Cork's cannon armed Sea Hurricane as "his" aircraft, even if they miss the fact that he flew two diffrent aircraft during the day. If Osprey's FAA in WWII is stating that his regular mount was 7*L, then the chances were that this is referring to Z4642. But what about Z7093? There is a chance that this aircraft could have been 7*L, but being a quick replacement while Z4642 was being repaired, this aircraft has not been as well documented and probably is not being considered as Cork's aircraft in most books, if it is mentioned at all. Because of this, I will probably go with 7*L for Z4642 until I can get better information. Even the two sections from the book I posted here don't include the squadron codes.
There is one thing that might help this. There is a biography on R.J. Cork that has been printed in England. I have not been able to get my hands on a copy as of yet, but if anyone has this book it might have information in it that could solve this question, on top of just being a great book to read.
Again, thanks for all of the help!
Glenn