OMG, poor little precious kitty, poor you for going through such a terrible experience. Here in Montreal, during the winter months, a lot of people bang real hard on the hood of their cars before they start them up in case there is a cat trying to keep warm under the hood. I'm surprised that he was under there is such hot weather.
Bless you for caring enough to help this kitty as others would have just driven away without a care in the world. You're an angel.
It definitely sounds like an abcess on his neck and I hope and pray it heals well.
I agree with keeping the name "Lucky" cause this adorable kitty would not have survived if it wasn't for you.
Good luck with him and please keep us posted.