It looks like there is an inner and outer rocker, the piece you're looking for to me seems to weld to the inner rocker and drop off to the floor pan. I did a front patch on my passenger side floor and the pan I used is attached to that dropoff. On my drivers side, I had some rust on the drop right behind the seatbelt mount, i cut it out and there's also an inner reinforcement welded behind it. The inner piece had some scale but cleaned up and is solid, the outer was a small enough section where I just fabbed up a patch. I've seen floorpans and the rockers but if these floor drops and reinforcements are being made my feeble searches have not found them.
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