I glued in the doubler for the top bearing mount. the wrenches are to hold the plate down so the glue can make good contact. I made a lower bearing plate and glued on a doubler where the bearing will mount. The lower plate was dropped in with a reasonable fit. (not too tight) When in place, I drilled through the top plate until the tip of the bit touched the lower bearing plate. The lower bearing plate came out and I finished drilling the two holes one at a time. When I mounted the bearings and dropped the lower plate back in, the tube slid through the two bearings with no problem. The alignment was worrying me for a while. I disassembled the top bearing and glassed the lite ply top of the box to harden the plywood. The way the bearing will go in, the screw heads will be against the light ply.