Put a set in a buddy's 77 and they fit just fine. This was with a 2-into-1 setup though. In setups like that, I don't see why the transmission would cause any issues with shorty type headers anyway.
The bellhousings are stock and the pipes cross over before the trans anyway. So no problemo.
Clutch linkage changes, automatic transmissions of certain designs, different t-cases and front axles, maybe. With true dual exhausts and any of the above? Definitely a tight fit. I can see possible issues then.
But with shorties and a 2-into-1, I think you're good to go.
Which way are you thinking?
Paul