The wood "runners" also help prevent squeaks and wear as the bed and frame flex and twist. don't do it like my 62 is-the PO welded the back of my bed to the bumper and welded the bumper and the front of the bed to the frame.
Speed

1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck