I have a dumb question: Do you have the shift cables?
There are several ways to measure but you can call grady and as what their records show. One way to measure is to actually pull a drag line from the helm to the stern all the way that the cable will run right into the motor and then measure that rope. You need to know how the last few feet will be routed;in a rigging tube or loose in the well and if looped or not. It will help to see if someone here can post a picture of there motor rigging.
Of course the cables for twin motors will be different lengths so you will need to measure both
The second and maybe not the most accurate way is to estimate the cable length from above by measuring the run from the side of the helm to the stern and then adding estimates of the length of the cable from the side of the helm (near the rigging tubs) to the control box and adding the cable length from the aft end of the rigging tube through the motor rigging tube and into he motor.
I suggest you call Grady, get their numbers and then do your own estimate and see if the measurement agree.
