Ted,
Yes I have changed the rear-end behind my '54 Chevrolet 3104 Hydra-Matic pickup to 3.55. This truck is in the middle of a complete restoration, so it might be a year or more before I drive it.
The 3.55 in my 4-speed Suburban convinced my that the conversion is worth it (even though the increase in speed, decrease in RPM, is only about 11%).
A friend who has a 53 GMC 1/2 ton with a Hydra-Matic changed his rear end to a 3.55 several years ago. He drove that truck on a 5,000+ cross-country trip a few years ago. He'll be driving it to the ATHS show in South Bend this spring (from Boston).
I'll take my chances with the 3.55 behind the Hydra-Matic. And, if I am wrong, I have a spare Hydra-Matic rear-end that I can swap back in (I'd be willing to bet that I will not need to do so).
