I have the seat frame built and placed, bolted using seat mounting bolts (6 of 8). I plan to paint the bottom side of the frame and the floor area that will be covered prior to welding in the frame. The plan is to weld the frame to the remaining original seat riser at the rear, the door latch posts, as well as the floor at the front edge of both cross angles. The inner front seat mounting bolt area is high enough above the floor that nuts were welding into the frame rather than going through the floor. The rear seat mounting bolts required a single washer on the bottom of the frame to make up for the thickness of the cross angle, but the outer front mounting bolt locations required a stack of 6 washers to be welded in place as a spacer to make up the gap to the floor. All bolts that go through the floor are being secured with large, thick fender washers to spread the load on the floor. I had considered welding the washers to the floor but have decided against that due to concern that the welds would cause more harm than good.
Once the seat frame is welded in place I plan to remove the cab from the frame to allow the bottom side floor and cowl panel welding etc. to the cab as well as work on the frame.
