So today at the workshop while I probably should have been doing other things I popped the hood for a look. Typical 70's build... lots of greencaps... looks pretty tidy! Schematic was easy to find because as far as I can tell they made like 50 bajillion of these things. So I worked out where the pres go into the mixer section and re-routed them to direct outs on the back. There was enough useless connections on the rear for me not to have to drill any new holes... this is good, metal work is annoying.
I left the last pre (number 4) in the mixer section, so the fourth pre now has extra gain and can kind of be driven by leaving the output down and the input up.
Results? I don't mind these things... they have a kind of pronounced midrange that I can see working on guitars and some drums... awesome!
Here's a snap of the rear where you can see the 4 jacks I added for direct outs






