Don't discount the 3/4 ton truck! Best modification for highway driving is changing out the rear carrier to a 4:10 from a late 1960's or early 1970's 3/4 ton pickup with an Eaton rear axle. Ring and pinion are one unit and is an easy swap. Also find a Borg Warner T5 transmission from an early S10 pickup. This will give you overdrive and easy cruising and will get your engine rpm's down to around 2100 @ 60mph.
