The new SLO has 4 preamp tubes lined up in between the output transformer and the choke, plus one tube next to the output tubes.
The older ones don't have this same layout.
Regarding the new SLO's, I'm assuming the preamp next to the output tubes is the V5 position.
Wanted to confirm.
From the info I've gathered the layout is the following
V1= OD/CL
V2= OD
V3= Cathode Follower for FX Send
V4= Cathode Follower for FX Return
V5= PI