I have a ‘57 3200 that has the 89” long bed step side. I’m getting a 98” fleetside bed off of a ‘58 3600. What all do I need to make the swap work? I’m assuming the mounting is pretty close, but what makes up the 9” of difference?

1957 Chevy 3200
1971 Jeep CJ-5
1983 Chevy K-10