The floor of your 40 is the same as a 46. My floor was solid. I took mine out and the floor was fine (a lot of spot welds). There are two large holes for the gas tank. You can make disks and weld them in or go to a home center and look at door handles for closet doors insert type for bypass doors. The carpet will go right in from the back of the cab up to the firewall. The 1 inch or so drop in the floor for the gas tank makes it right for the bucket seat with the base to bolt in.