I think the easiest and cheapest would be to pick up a set of 16" wheels and a decent used set of LT235/85R-16 tires for it. If you're running a 4.10 rear end,you'll be running about 3,110 rpm at 70 mph,that comes down to 2,900 rpm at 65 mph. You'd probably be into it under $200.00
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