Here's my experience so far.
I have a '59 half ton with a 283 V8, so it should be the same as your '55 2nd with a 350 for header fit. When I bought the truck, it had a set of no-name old rusty headers on it.
The problem with headers on these trucks is that the steering box is very close to the engine on the left side, which doesn't leave much room for headers. The headers on my truck didn't really fit, so whoever put them on had beaten them with a hammer to dent in the tubing a little to clear the steering box.
I decided to replace my headers, so I bought set of Headman headers and took it to my exhaust shop to be installed (can't do this myself because I don't have welding equipment). My exhaust man told me that the Headman headers would not fit either, so I returned them.
On advice from this site, I bought a set of Sanderson headers, model CC3, which are blockhuggers. You can check out their site at
www.sandersonheaders.com I haven't yet installed them, but when I bought them, I was assured by their sales person that they were designed to fit my truck. We'll see; they just arrived a couple of days ago and I haven't put them on yet.
LT