I assume you want to keep your engine have it rebuilt VS. a block replacement. The first link is a rebuilder of your engine. The second is a replacement block builder. The second is around 2800 based on your cars year (hum cost more for a 55).
(If your block is shot then your stuck with replacement)


http://losangelesmachineshop.com/tag/chevy-gm-235-long-block-rebuild/#.VbeOqbeRjgp

http://remanufactured-engines.com/Chevrolet6.htm

Cost can be high, but like a good doctor, finding a shop that has experience in the 50's I6 and turns out a great engine is better then picking a cheap shop that does not know that engine and gives you a headache months later.

In addition there are rebuilds and then there are rebuilds. A shop could just disassemble hone a few things and slap some new rings in and wham you have a rebuilt engine. Or a shop that can spend time and effort to check and true all surfaces, inspect all parts and replace every worn piece. That cost a lot more but nearly fresh new engine is much better then a warmed over one

Baking in the nice desert sun, breathing life back into a 48 3800 5 window.