Try this link
http://home.comcast.net/~jon.held/
I know it's not for a dual battery setup but Jon Held took out the smog pump and plugged the ports to get a York air compressor where the smog pump is.
As a result of having OBA that area is clear to put an FZJ80 battery tray in the location, if you take out the exhaust fan.
I'm actually going to put a York in the engine bay as soon as it gets warmer. This will free up that area for a dual battery for me also.
Here's my question to Jon about the system:
1. What ports did you block to disable the smog system?
"None. I removed the air pump and the hose that feeds the flying saucer air
valve. I used the intake hose that comes from the air filter housing to feed
the York."
Maybe this will help, maybe not.