55.2-59 Searching for Overdrives

[SanJosesSteve]

My 59 GMC is still running around with its original 270 mated to a 3 on the tree transmission. I love the 3 speed for driving in town as I don't have to shift very often. I think adding an overdrive would really go a long way to make the occasional freeway jaunts more enjoyable.

What am I shopping for? What should I expect to pay? Is it as easy as searching for a "Borg Warner R10 Overdrive" ?

Is there a specific model I'm looking for to mate to my existing (recently rebuilt) 3-speed? Can I even do that or am I shopping for a complete Trans/Overdrive package? I really want to keep my original transmission.

Anyone know of a shop that sells these as rebuilt units or am I destined to wander the local wreckers looking at drivetrains?

The 400 mile trip I made last summer in it would have been way better if I could have brought the RPMs down while cruising the highway!

Thanks, Steve