Alignment Tool
In order to measure the benches I had to make a special measuring tool.Expandable from 4 to 7 feet
This easy measuring tool will help to align the bench mounts.
Material...
I used 2x 4 foot pieces of oak. Then drilled 3 1/2 inch holes. Both ends and one at about 10 inches.
Router Work...
Then I "routered" the longer distances a 1/2 wide. 
2 Bolts and done...
2 bolts, 2 washers and 2 wing nuts complete the assembly. The 2 pieces are aligned "mirror" to each other. Then the bolts are inserted through the slots. Done!