I had a Petter (AC1W or AB1W) on my Catalina 27. Spent lots of time messing with it....
I don't recall any funky shifter stuff, but if you posted pictures, that might help...
Have you tried to get a manual from lister-petter?
1987 CS 36 Merlin "Kyrie"
"They drove a dump truck full of money up to my house. I'm not made of stone!" -Krusty the Clown