Factory headers 69 dart swinger 340?

They were likely installed at the dealership,

The Hustle Catalog recommended changing to a LD-340, Hooker headers, and 3310 Holley, IIRC all had a Mopar Part#s, and were avail over the Dealer Parts counter.

At the dealership I installed a few "Hustle" items, before delivery to the customer,, and Mopar warrantied these changes..

I installed them on my own car upon purchasing it new. (1969)

I still have the Manifold and carb, the headers (under-chassis) wore out.