My truck is a 3600 with a different arrangement so it has a floating sill, but it has one additional sill due to length that a 3100 does not have. The photos on my page of the green bed being assembled are for a 3100 I found them in an article years ago. Follow those and the Mar-k information and you will be set. On my truck when I finally finished it I actually removed the floating sill since I don't ever load the bed heavy. The floating sill was designed for a very heavy load to compress the bed until that sill contacted the frame. In my trucks new life it will never see that demand.
