Header pipes (the ends into the cyls) are different, the exhaust pipe holders are different, 74/75 pipes will fit early frames but the underside bolt mounts to frame won't fit without making some brackets or re-welding them (like I did on my 72).
The pipe rear-brackets are HUGE and the holes won't lineup either -you'll need to oblong them. And the pipes stick out a lot longer and some here would say look like crap.
Repo decals carries quite a bit including early year complete sets
http://www.reproductiondecals.com/default_frameset.html?content.html~main