They became mandatory on cars and light trucks after 1975. Anything before that year that were already equipped from the factory must keep them. Heavier GVWR 3/4 ton and 1 ton trucks were phased in later, my 1978 K30 did not come with them from the factory.
Your 83 did come with them, and should have them on to pass inspection. That said, rarely does a inspection shop even question you on an older truck like that. Unless they have been busted for not checking and are scared to have it happen again.
and replaced with a straight through tractor muffler, oh about 10 years ago because it was rusted and just an old farm truck). There may have been some weird conditions set out for import vehicles at the time as it did take a few years to phase in. Some cars had them before 75, but 75 was the year it was mandated on all cars and light trucks in the US, this was also the year lead gas was phasing out as lead gas would kill the converters. My 78 K30 did not come with converters as the heavier trucks were exempt for a few years, much like 3/4 and 1 ton trucks only have safety inspections and no emissions inspections today.