The cast iron manifolds from Hooker or Sanderson are probably your best bet. Summit has something similar too.
If you are willing to use a cast factory manifold, I've heard that the Trailblazer SS manifolds work well.
Pacesetter Headers is here in Phoenix and they let me try GTO, Camaro and truck LS headers. They all either interfered with the frame rail or hit the stock clutch/brake linkage.
Here's Pacesetter's Camaro shorty headers on the passenger side-
Here they are one the driver's side - they would have worked but I had a manual transmission and wanted to use the stock pedals, but the linkage interfered on the clutch
I found some cheap LS shorty headers a friend of mine was selling at the swap meet and tried those too. These would have worked with a three-ujoint arrangement, but they looked like hell and were 1.5" diameter primary.
Ultimately, I decided I'd build my own - you have to be some kind of masochist to do this, but i wanted long-tube headers with a simple two-joint steering and would clear the stock clutch pedal.
Here it is in mock-up before welding. You can see the space in the middle for the steering shaft to go through.
In the chassis
Mike Finnegan has a YouTube video up on building headers. He shows a bunch of fancy tools and makes it look harder than it really is - you can replace all those tools he uses with a belt sander, a Sharpie and a worm clamp.
https://www.youtube.com/watch?v=Vr-nraY0rsE