I'm not sure how other builders wire the cabs they make but
the Marshall 4x12 I have is switchable Stereo or Mono, Set it
Mono it's either 16 or 4 ohms, and set it to Stereo it's 8 ohms
per side.....It also depends on the ohms of the 4 speakers you
have in the cab-If the 2 input jacks on the cab are 16 ohms
each you'll set the head at 8 ohms, If they're 8 ohms each set
the head at 4 ohms..........