I know he only used the rhythm channel of the Soldano and a Marshall Guvnor pedal for additional gain.
As someone who was lucky to see Gary on most tours from Run to Cover in 86 onwards.
Don’t estimate how loud he played. First time I saw him a friend who went with me fell off his motorbike whilst stationary the following day, because the volume had affected his inner ear.
That mind numbing volume whilst absolutely insane was very much part of Gary’s sound.
I’ve got no idea how he controlled it
I think his pickups also make a huge difference to get that sound. I have never able to get the exact same sound as his on my Les Paul (although it can get very close with the right amp and cab) and couldn't figure out why until I realised he was using out of phase PG Blues pups in his CC#01 guitar.
This article gives a little more info on them. I am very tempted to get those and install them in my fav Les Paul, but haven't made the jump yet!