His main amps were 4 hole Marshalls so “master volume” is effectively on 10 the entire time. It’s not a ton of preamp gain, but the power amp is compressing, the speakers are breaking up, and you have infinite sustain and harmonic feedback from playing that loud.
So it’s definitely a lot less preamp gain, but it also has two other things going on that most modern recordings don’t have. I assure you though, George could plug into an Axe Fx and play this song today with insane amounts of gain and you’d still love how it sounded, and you’d still be able to tell it was George playing.