If you want the truck to last, my suggestion is to take care of this surface rust as best as possible. This depends on the amount of work you are willing to go through to take care of it. Here is my suggestion, though.
The easiest way to take care of this would be to use a rust encapsulator such as POR15. Products like this bonds with the rust, stopping it from deteriorating any further. It also covers the area to prevent new rust from forming. To best use it, I'd separate whatever parts you are trying to coat and getting it between the parts so as to keep the nooks and crannies as pristine as possible. This is the "work" portion I'm talking about. More than likely, just coating the exterior spaces (the facing parts of the body with rust on them) is going to bring some extreme life to your vehicle in and of itself.
There are some caveats when using POR15 (and I assume others like it).
First, direct sunlight will deteriorate its effectiveness. Since this is inside the vehicle, it really doesn't matter. The second thing to worry about with POR15 is, wherever it goes, it's there for life. Use a throw away paint brush to apply it as it will never come clean. It will also bond metal together. Don't get it on the threads of bolts or in nuts as it will never come apart again without destruction. Also, once you start using a can of the POR15, use what you're going to use and throw the rest away. The reason for this is, once the stuff gets into the seal portion of the can and you put the lid on, as soon as it dries you'll never bet the lid off again.
I wouldn't worry too much about the cast parts like the steering linkage. Those parts will still be held together long after the truck has served its useful purpose. It takes a long long time for cast iron to deteriorate due to rust.