You can give as many reasons as you like. I would definitely mention the science and drama. Back up with evidence wherever you can e.g. letter from teacher on his ability, any noteworthy prizes, letter from extra curricular leader if he does any relevant clubs.
Our primary head wrote a letter which was incredibly supportive.
We also included examples of DSs work in the areas that the wanted school specialises in.
We looked at every extra curricular activity and every subject offered. We compared all the stats available.
The ethos of the school suiting you is probably something that everyone mentions in appeal but stand out, be specific and give evidence wherever you can.
The being close to home thing seems to be huge - that's my interpretation, and it also ties in with his anxiety.
Go in and fight with everything you have. Nothing to lose. If you are unsuccessful, you can get on the waiting list or even apply again in year 8 when the odds are better.
Don't lose hope. I think you have a very strong case. Sell it for all you are worth.