Mount 55lbs tv on 2x3 studs
Looking at the manual, it looks like the top mounting points are about 1' above the bottom mounting points. If you have that 55 pound TV at the full extension of 2', then that means the top mounting points will be pulling directly out from the wall with double the weight of the TV, or 110 pounds. Guess that someone will lean on the thing, or your cat will jump on top, and you should plan for at least 200 pounds of pull on those anchor points (100 pounds per screw).

I doubt that a single screw in a 2x3 can reliably hold 100 pounds pull straight out from the wall. That, plus the info that you need a 2x4 cavity to use that power bridge, leads to the following suggestion:


Cut a 1/2" plywood panel large enough to support the base of the OmniMount, plus a few inches on all sides
Bevel the edges of the panel to make it look more planned/streamlined
Cut a hole in the middle of the panel for the power bridge, expecting to mount the bridge into the hole, rather than into the wall, so you have the needed extra depth
Cut a clearance hole in the wall for the power bridge
Mount the panel to your studs with plenty of 3" lag bolts
Mount the OmniMount to the panel
Mount the TV to the OmniMount


It's possible this is overkill, but wouldn't you rather be sure your lovely new 65" TV didn't become a YouTube-able lesson?