I have a set of cheap headers on my magnum 5.2 in a duster and there are several interferences and I have a feeling they're going to blow gaskets frequently. Id like to replace them with a good flowing set of exhaust manifolds. There's no way I'm paying for a set of HP manifolds from a 340. Will any factory Magnum or early Dakota manifolds fit? Thanks for any help.

I would think that they woud hit the firewall & not clear the steering shaft on the drivers side. I'm sitting here right now looking at the HP's & the Mags that I'm putting on my RC when I wake in the AM. Spend good $$$ on a good set of headers with those aluminum layered gaskets

Why not buy a GOOD set of headers that fit a small block in your car?

Wow... this question is right up my alley!
I tried this very thing. 1974 Duster. 360 with a 4 speed and power steering. The RH manifold fit and cleared great. In fact, with the outlet right above and behind the oil filter, this manifold saved 2 bends in the exhaust pipe further increasing flow. The LEFT side? Uhhh...
NOT good. The manifold wouldn't fit around the power steering box. Having a manual setup may have helped, but the outlet was too close to the clutch cross shaft. The only possible way that i could see the rear dump LH manifold to fit is MAYBE with a manual steering box and a floor shifted automatic.
I ended up using a '68 340 manifold on the left and a Magnum on the right.

I tried them on my 68 cuda and they fit great, they were the 618 and 619 casting big outlet ones. My car had manual steering and a colum shift 904. The bend off the left one was a little tight but not bad.