Question, I see you're from Sac, Cali. So do you live in area where smog testing is required? Cali emmisions is going to be different. Do you have a Cali emmisions truck? Because of of your GVWR and if a Cali truck it does have a Cat Converter right? And an Electornic feedback carb with a CCC (Computer Command Control) system for the E carb and ESC (Electonic Spark control) as well as EGR and probably a AIR pump aka Smog Pump with a dirverter valve right??? So I doubt you want to tell the smog testet that it's a 400 from a 70's truck if they don't figure out or you might have to see the referee.
So if all I'm suspecting above is true, we need to find an 86 K10 Cali Emissions Vac Diagram and make sure it's set up that way so maybe the smog test station wont think nothing of the engine that's in it. And hope it's in good enough shape to pass tailpipe sniffer test.
Had it been a K20 or K30, you might have made it without a Cat. These years the difference of emissions on the trucks was very different based on GVWR. 3/4 tons and above got by with much less than the 1/2 tons. Also passed with a dirtier tailpipe sniffer test.
