I've used the approach with Corvette exhaust that Dan suggests - it worked well. The thing with the Corvette exhaust is that they are double-walled stainless (for noise reduction, I assume) and it is a little tricky getting the downpipe grafted onto them, but can be done.
Pacesetter headers was in AZ and they let me try a bunch of different long tube headers on my '49 GMC - Camaro, GTO. truck - but I couldn't find anything that cleared the frame rail, didn't interfere with the stock brake pedal and I could snake the steering linkage around.
So I fabricated headers using the 'header legos' from ICE. I bought a 1.75" kit for about $400 from them and sold it on ebay for $300 after I finished the headers. You don't really need to model both sides and you'll find you model just a couple tubes at a time.
Here's a picture of the headers being fabricated on the bench - I used stainless mandrel bends/flanges- they are not equal volume by any stretch - maybe within about 20%
Here's a trial fit of the tacked headers on the truck - the open space in the middle with the tube sticking up is where the steering shaft passes through them. I built the headers on the chassis, and I found that when I went to fit the inner fender wells I had to put some relief pocket in them to clear the headers, but the headers will come in and out of the truck with the body on.
Here's the header installed on the truck form underneath-
I tacked all the primary tubes with a TIG and took them to a shop to have them welded, then took the flanges and collectors, but them on the engine, tacked them in then returned them to the weldor to finish. Cost me about $250 to have them welded up professionally
I'd guess I have over 200 hours in them and about $800 in materials/coating plus the cost of the pro weldor
If you think you'd like to try making some, LMK and I'll write up my tips and tricks I learned.