I have an 86 GMC 4 x 4,1/2 ton truck that is completly stock with a 350 engine. I want to either trade out the motor or rebuild it. I can do the work myself but I am unsure of what to match up for the internals. I am pretty sure the carb is a Holley Economaster. I want to pull a camp trailer with it also. I live in California so it must pass smog. Any help would be appreciated.