I found it interesting that the photos in Waldo's (most excellent) magazine clipping shows a mixture of cabs with the magic tone-enhancing speaker clips, and cabs without.
Damn clips...must be made of some space alloy.
(Edit) I was attempting humor, but I just re-examined the schematic prints. The earlier print shows speakers bolted into the cabs. The later prints show all clips. This might be repeat info, but I would presume that in that period is when they discovered that the clips made the speakers easier to change.
(2nd Edit). Wait. Wait. Not so clear cut. The early photos (w/ speaker covers) have both bolted & clipped.
Curiouser & Curiouser. The world just keeps getting Curiouser & Curiouser.