Good old 2-into-1 exhausts. 70s were a tough time for cars, especially anything "performance" wise, it just wasn't happening. The last "icon" of American Muscle being the Bandit style Pontiac Trans Ams, and those were only rated around 200-220 HP with a Pontiac 400ci. I have a 1979 Pontiac Firebird Formula with a 301ci Pontiac motor, and it has a identical displacement and power ratings of the Ford 302. Now, my Formula came from the factory with 2-into-1 exhaust, and it was pretty repressive. You'd floor it and the car would chirp sqeak and roll on. I had a dual exhaust with an x-pipe and glasspacks/2.5 inch piping installed and now it'll burn rubber in Drive. That really showed me the difference between single and dual, everyone knows that dual is more "power" but this experience really put it into context for me.
I have a 79 Granada 302 and my intents were to switch to headers, true dual exhaust, and a 4bbl set up. I'm not touching the motor until it kicks the can. It's got 149,000 original miles on it and it's still ticking. I have Fox Body headers from my old 1992 Mustang that will likely fit, and I'll just build an exhaust set up.
If you get yours done before I do mine, please post and let me know how it went/like it/power increases/MPG and so on. I'd love to hear what you use! Oh and any way we can see some pics of this LTD? I'm a big fan of the 70s full size cars.