When we get the new emissions here EGR will be required. Basically anything that came with it needs to be there.
In California the CURRENT testing for SyTy or any full-time All Wheel Drive is what they (here) call a Two Speed Idle. Checked at 2500 RPM after 180 seconds, let it drop to idle and then checked again after 60 seconds. There is no EGR at idle. The tech is supposed to pull on the diaphragm, and the engine should stumble, but the valve does not open at idle (with stock calibration).
Smog-legal engine swaps in Emissions Inspected vehicles (currently 1976 and newer) need to be an engine of the same year or newer than the vehicle. You can not change Gasoline to Diesel, or Diesel to Gasoline, but you can convert either to CNG or LPG. The emissions criteria used will be for the year of the engine, and sort-of the model of the car it came in. If CO is adopting our smog inspection program, your '59 should be clear regardless of what engine is in it. Not even CA cares about 1975 and older any longer.
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I'm a California Native. You'd be hard-pressed to find a more conservative right-wing Patriot than myself. People forget that California was the home of Regan, and that he was our Governor from 1967-1975. Politics in the state have changed, and now Sacramento is inhabited by lunatic liberals. ( I wonder if Nello has moved over there yet? He'd fit right in.) Other than the two coastal metro areas (Los Angeles and San Francisco) most of the state is still predominantly Red. The Reds are outnumbered by the Blues 2:1. The migrant Californians are probably the same ratio of taking their voting habits with them when they leave. Not ALL "Californians" are liberal-voting retards. Certainly not I.