Further, if you decided that you wanted to keep that engine and it is not compliant you've likely got some expensive parts to buy. I went through this with the YJ from Hell.
OBD II engines have to be completely original, excepting CARB E.O. numbered parts for
that engine's original application, from the first sensor in the intake tract to the last sensor in the exhaust system.
Say that you're claiming that this is a 2003 5.3L C1500 engine. Any E.O. numbered part has to be exempted for that truck. If it is exempted for that engine in some other application, but for that truck then it's not a legal part. All the rest of the parts and the configuration must also match that truck's original configuration. If you start out with all of the correct parts and they all fit the new chassis it's not that bad of a job. These are the kinds of laws we get when those writing the laws to get themselves re-elected have Zero mechanical understanding. No, I'm not jaded.
I don't want to turn you off of the truck if that's the one that you really want, but I do want you to have an idea of what you might be up against.