Looking for the stock exhaust pipe that connects up to the heat riser and and goes down towards the cat. I have a 79', not sure what other years had this configuration.
if you want stock, it was a 79 and 80 only, it had 2 smaller pipes that came down to the cat, it had an adaptor piece on the bottom of the manifold
you can use the later single pipe that was used for 1981 thru the end.
I've got a complete stock setup from manifold to cat if interested