Classic/Antique Car Repair: 55 chevy truck rear end questions, 55 chevy truck, liquid wrench

Question
I have a '55 chevy 3/4 ton 2nd series truck with a 4.57 rear end ratio.  I'm luck to be able to go 55 mph with the truck.  I would like to be able to cruise smoothly at around 65 mph.  What options do I have as far as getting a better ratio in the  rear end (swapping rear ends, swapping pumpkins, overdrive transmission)??.  I've heard of people just swapping out the pumpkins from other trucks-does that really work?

Answer
DAN; I know how you feel I had a 5.13 in my s/s and all I could do was 55.
  you can  just pull your gears out and replace them with some 3.90s than you can cruse.You can remove your unit.and just replace the ring and pinion and bearings if needed , also shim the back lash if need be too.  you should have no trouble with it. just spray up all bolts with liquid. wrench. check out (summit.com)  and (JC Whitney .com) for the gears.