In terms of head, there are only two slightly different but basically the same chassis mounting: bottom mount (most heads) and top mount (fender and epiphone) Basically the same.

However, for combo, I notice that there are three styles:
a) Top mount, control face forward, tubes pointing down (Fender black face, silverface, and most combos)
b) Back mount, control face up, tubes pointing down (Fender hot rod, Vox)
c) Bottom mount, use wire to hook to controls. Common in early 50's construction.

Is there any particular advantage in terms of chassis mounting (for a combo)? Obviously for sound the mounting would not matter, so I am particularly wondering in terms of usability, construction, and modification.
Top mount is the way to go, in my opinion. That's what in my VJ copy, and i can'y imagine it being more conveient than this.