OK - sorry for the multiple posts - but I just wanted to share a few things -
First - thanks to everyone here for helping with everything.
Second - installing the shakers was a breeze - easier than installing them in my sofa for sure IMO
I was able at lunch to:
1. Cut 3 boards approx 15 3/8 inches long (used 1x6)
2. Test fit boards (tight fit but not "forced" tight)
3. Screw shakers to boards
4. Install boards in Berklines
5. Do a quickie hook up and TEST!
One side of each chair was a simple breeze for me on the boards, as I only have arms on one side of each chair. I used a stubby screwdriver to do the other sides as posted before - I just drilled some pilot holes first to make it easier.
Very very nice. I am sure the shaking will be more solid now since I have 1 per seat (versuis just 2 in my 8' sofa before) Just the test (with seats laying on their sides) seems to have a more solid shaking feel when I put my hand on the seat.
One note: It was WAY easier to do this with the backs off. I guess thats obvious but I almost put the backs in my rush to see what they looked like in the room.
All this took me about 25 minutes.
I will post pics also tomorrow.