OK guys - I got the following from Don Underwood:
"Thanks for your inquiry Roger.
The suggested setup has the mid cable transducer on the G side of the bridge. The end transducer then goes on the E side.
The reason for this is to orient the transducer cases so that the internal damping pad is on the wing side of the case. If you install the pickup the other way, so that the output jack is connected to the E side, the transducer cases are turned over, so that the damping pad is on the leg side of the case.
The purpose of the damping pad is to reduce finger noise so the pickup may sound a little "tackier" this way.
It makes no difference which way the jack is installed on the tail piece except that the label on the jack is more visible.
Thanks for sticking with your Underwood!
Best regards,
Don Underwood