I would go with the junction and fit it in place with everything. I don't know which headers work best but the mufflers should work great. You could take it up to the local muffler shop and get their opinion. I plan on putting headers on some day so let us know what you end up doing.

I was fortunate on my '73 -- no cats! As others have said, true duals are separate exhaust from the exhaust manifold (or header) back through the muffler and out the exhaust pipe. As far as headers go, I upgraded my engine to AFR heads. When talking to AFR, they told me they wouldn't sell the new heads unless I had some type of headers because of the big improvement they provide. I've got Hooker (Competition). They were supposed to be a direct fit but only if I didn't plan on turning right. I finally got a shop to carefully custom bend an added clearance of 1/2" so the steering gear didn't come in contact. I've never had any problem with bolts coming loose, but added Stage "8" locking header bolts anyway. When I re-did the exhaust, the shop said they could add an X or H pipe but unless you regularly keep the rpm's over 6,000, you probably won't see signifcant performance improvement although you might get a different exhaust sound. Hope this helps.

My 75 has a cat on it. But the 74 frame is the same. So when I replace the exhaust, it will get the 74 true dual stock system in place of the 75. Other goodies may come later when the engine gets beefed up a bit, If I do more than install another cam. If I only do the cam, the 74 exhaust will stay. I like the sound.