Hey, I've got a very restored 66 k code over in France. It's got a 4 speed. and I believe its got a detroit locker differential. The person who restored it must have used a 3:90 (or more) rear end, as in 4th I'm cruising at 4500 RPM at 80mph. The problem is that normal highway speed is 80, so I think I would need to change it for a more reasonable cruising RPM. What would be the best compromise to not lose too much low end power, yet be comfortable on the highway? (it's got the original 9" rear end).