We just completed the intstallation of our Lagun Table mount using our original table top too. Instead of mounting in the middle of the table, we positioned the mount perpindicular to the rear dinette seat and marked the table as it sat pretty much in the same position as the locked default with the OEM pedestal. It still rotates in for more room in the galley and can also rotate out for lots of room in the dinette space. For the bed mode, we made sure to mount the base far in enough so that the table top can still be rested on the sides and back seats. We will look for some kind of short table leg or tension bar to help support the middle outer middle of the table in bed mode, but it seems fairly stable once it is set down and the cushions placed on top.
We bought the predrilled extender from Marine teak, but it does not clear the cushion as nicely as yours. I think we will add the two plastic shims to bring it out a bit more. And of course we moved the power plug.
One more thing to keep in mind for those considering this upgrade. When you open up that rear compartment to move the plug and install the bracket, consider fortifying that cross piece to stabilize the table installation. We still have a slight wobble and will probably screw in some l brackets on the cross piece and some additional white screws through the front of the rear base into the cross piece.
Airstream cut our middle brace a bit too tall, so for the rear seat plank to sit down flush, the brace is leaning to the side a bit with only one screw holding it into the trailer wall. We are going to shave that down a bit when we go back in to install the L brackets and additional screws.