Drum was only with the A model, E model had digital computers
you had to kick it so that the drum spins again, that drum has the whole computer program / algorythm for action written on it and needs to spin so that the computer knows what step / calculation to do next
the A-6E then finally got solid state electronics, that not only where ALOT more reliable (carrier landings tend to damage the drum) but also faster with more computing power.
Yes
A-6A was rated to carry AIM-9D
A-6E is rated to carry AIM-9D/G/H/L
A-6E TRAM / SWIP have AIM-9H/L/M
sidewinders can be mounted under all 4 underwing pylons