Accord to Gibbon's tech, Elwood Francis, Billy has since streamlined his rig somewhat.
From a February 7, 2020 Interview"
"Billy's guitars all have the shorter Gibson scale length, including the Tele-style guitars...."

To the left and right of the stage is a large Magnatone amp stack, which is largely used for visual purposes: Only two outer 2×12" speakers are fed with bass and guitar signals - for monitoring for Billy Gibbons, who is on in-ear - Use waived. (Image: Nicolay Ketterer)
Above the Marshall rig are two iso boxes fed by the Marshall and Magnatone signals. Each Eminence 1×12” speaker is picked up with a Royer R10 ribbon microphone.
“Billy uses his own Eminence signature speakers for live use, which are not yet available. The speaker is based on the 75 watt Governor model. Due to the headroom, the low-end is retained more clearly because the membrane is moved less than with a less powerful speaker.”
Do not comb filter effects significantly alienate the signal in the closed box with the insulating material? "Sure, a speaker in an enclosed box doesn't sound like a speaker on stage! The amps aren't massively cranked - that helps. It may not be ideal, but it sounds exactly the same every concert - a compromise in terms of consistency.
The current cabinets from Voodoo Amplification sound much better than the predecessors from another supplier, and they are also only half the size.” However, the Iso-Cabs have a long tradition at ZZ Top: “When I was still looking after Joe Perry's guitars at Aerosmith , we heard from Billy Gibbons, the first to use an Iso-Cab: 'Cabzilla', a huge road case that housed two miked 4×12” boxes – practically an encased full stack. Get that in a little club!”