Toyota Sienna reclining cockpit seats

The new bases are 16 gauge, folded and welded corners, the center pivot is made from nesting schedule 40 pipe, with the bottom cylinder welded to an 1/8" shallow channel reinforcement which is welded to the sheetmetal base.   The top cylinder is welded to a steel plate, and the OEM steel seat slides are bolted to that with button head cap bolts (stronger than grade 8). The center bolt is a 3/4" grade 8 bolt welded to the 1/8" channel reinforcement.

This arrangement allows me to buckle the seatbelt, unscrew one Nylok nut, and the seat can be lifted out by the seat belt. It makes it a lot easier to work around the engine or under the dash.  Because the 

All the cable-controlled seat mechanisms still operate by the original levers, except for the seat slide. The OEM slides worked fine once they were cleaned up. The pivot locking mechanism is visible at the front left corner.

The Sienna seats have integrated lap and shoulder seatbelts so I bumped up the 12 bolts to 3/8" and they all go through the plywood floor and aluminum floor framing.