You could retro fit. I drilled holes of varying depths into the hardwood bearers, approx 3/8th" deep at the rear, reducing down to almost 1/16th or so at the front. Then I "hacked" away at the remaining wood with a dremel until the two surfaces were roughly flat. I then bedded the retract unit onto a layer of epoxy and microballons spread onto the bearers, to ensure the frame did not distort as the screws were tightened.