cat on my 1979

[Nontwisty396]

I spent a decade in the exhaust business. Yours was a common question. Everyone (mostly) has steered you in the right direction.
The 2 most common and simple ways to tell is look for the emissions sticker, it will say "catalyst" or "non-catalyst" on it USUALLY.
The other simple way is to look under the truck. If there is a large (possibly wide oval shaped) heat shield above the exhaust around the rear of cab to front of bed area it likely had one.
IF the exhaust is original, look about 3 feet back from the manifold to see if there's a newer section of pipe around 2 feet long. That would indicate a "sub-pipe". But as said, most 3/4 tons and up didn't have one. And as mentioned, the newer hi-flow cats don't really hinder performance, especially when installed as a pair on dual exhaust. Spendy, but looks nice and balances sound as well.