Fine dust badge Chevy C1500 (just facts, no assumptions please)

Hi! I’m about to buy an 88 Chevy C1500. The car is registered as a truck and in the vehicle license is under pollutant class: “unknown”. Now I have heard that this car actually had a cat in the USA. But it flew out years ago when import, because it was not necessary for a truck registration. Well, now comes the badge crap! Possibility 1: Kat retrofitting. What’s necessary? Where do I get a suitable cheap cat? What tests does he have to pass? Do I then get a badge? Possibility 2: I read on the Internet that the Dekra has databases to check information about such US cars and there someone drove there, who looked into the data bank (instead of under’s car) and in it tand that his car actually (in the USA) has a KAt —-> badge, although no cat was under it (that this is not the most legal variant is clear to me). What else is there for Optio? Give me a hand, will you?