Rearend Swap for '55 1st Series

[tjf8801]

I'm new to this site and new to forums, so excuse me if I don't know the proper etiquette. There seems to be a lot of members with good knowledge, so I've got a question for you experts. I've got a 1955 Chevrolet 3100 (1st Series) that has the original rear differential. According to what I've read, it has a gear ratio of 3.9 to 1. This causes some issues on the highway, as my 350 V8 has to run at high RPM to stay up with traffic. What are some common rearend swaps that require only minor modification? I do not want to lower the vehicle or really make it ride better, I'd just like a lower gearing. I still use it to haul things, so it needs to have a pretty stiff suspension.

I guess another good question would be to ask what I need to look for in a prospective rear end that will make it fit correctly and function appropriately.

Thanks!

Ty