As long as it's a good motor and you don't care about fuel consumption, have no fear. I run mine with 5.38 gears on 33 inch tires. Around 3000rpm at 55mph according to GPS. I've driven it to cruisin' the coast twice, 240 miles round trip. Only problem was stopping every 80 miles to fill up.I drove my 70 Ford 302 at 70mph (also 3000rpm) to North Carolina (800+ one way) with no problems.
1958 Willys CJ5 on a 71 Jeep CJ5 chassis, 231 Buick, Dana 30 front, Dana 44 rear, lockers, 5.38 on 33" tires.