Thanks Chad !
The original front seats in the 87 CVX-16 are made of hollow blow molded plastic. When we got it, the bottoms had already been cracked and broken and so bolted onto 1/2 plywood through the base, not adjustable. WE want to retain the original seats, the upholstery is in good shape.
Solid Repair. Added 1/4" alum plates bedded in 5200 marine adhesive and screwed to bottoms. Then 5/16" rounded top carriage bolts with 2" fender washers through the seat, and through the plates. Added new sliders.