Because the parts I need on this one are smog exempt. If I "swap cabs"
my running complete '80 is suddenly a '75
Thereby relieving me of the ridiculous smog drama of my 42-year-old 4 cylinder truck that only gets a couple hundred miles a year and should be exempt anyway... Can't get replacement parts to keep all the smog equipment working as originally intended anymore. And if you get any original parts that are still in working condition, they quickly break once in use. That old rubber doesn't last long.