From what I remember reading basically they picked the gun then designed the aircraft around it.Engines were sited where they were to protect them from ground fire and the cockpit "tub"heavily armoured for the same reason.Apparently it can only fire in very short burst as the recoil if fired for too long can actually stall the aircraft.Could of course be wrong on all counts but sure I've read all that somewhere or other.Is the A10 not also called the Warthog?
Picked the gun .............. Basically yes

There was 2 aircraft that flew off against each other.
The Norhrop YA9, which wasn't picked but the Soviet Su 25 Frogfoot ended up looking very similar

and the Fairchild YA10.
The armorer tub which the cockpit sits in is apparently 23mm cannon proof but don't ask me to test it

Iirc, it was normal practice to open up the throttles fully unless in a steep dive when firing the GAU 8 so that the aircraft doesn't indeed stall.
Engines indeed placed like that for damage limitation purposes but also to help (with the help of the tailplane / rudder) to shield the exhausts Infra Red signature from MANPAD type systems on the ground
