Spent the rest of the day cutting away the rear pillar and rear cab mount to get started fitting the sill. The only thing to guide the sill fit is what remains of the floorboard flange aft of the seat riser, and that's pretty nasty... just barely enough to go by. The rear inner cab corner is rotted out on this side so the fore/aft position of the sill will have to be determined by the parking brake bracket that fits on the forward cab mount brace, so that has to be the next part that goes on.