how to adjust passing gear?

I have adjusted the passing gear on my 350 tran. and on my powergluide (chev.)but this old buick wagon is making me pull my hair**) ,from what I under stand it has a 300 cu. in. with a 300 tran. some call it a 2 speed power
gluide also,it doesn't have the linkage like the chev. it has wires on the
linkage that goes to the carb. and on down to the trans., I tested the
wires and all seems fine,where would I look for some kind of adjustment?
I can take pictures if needed, but juist thought someone would know.:confused: thanks