I would go with full competition headers (equal length long tube large diameter primaries, with no exhaust flange) and weld them up once you get them adjusted to your liking. I would then have them removed a exhaust flange welded up for use of mufflers, and then thermal coated as they are very thin and won't last long on the road otherwise.
One shot might be Lemons headers. Sorry I don't have their ph. # handy but they've been around a long long time doing quality work. Big name in custom headers. I'm sure even Big Dave's heard of them.
Not sure where you've looked but some of the more popular names don't always list everything they have. It would be worth a phone call direct to them just to check.
(eg. Hedman, Hooker, Kooks, Stainless Works, etc)
I think 'Headers by Ed' sells nice 'kits' that have enough pieces to let you tack-weld a set together, then you take them off and get them fully welded.
Word to the wise: be careful with Hedman- I got a pair for 67 Camaro Show Rod and they hung way below the frame rails and weren't tuned length. I ended up having my 25 year old Cyclones coated since they were tuned length and fit sooo much better. One would think a company as big as Hedman would build a better header with the reverse engineering technology available today.
My comments were more about the poor ground clearance offered with the Hedman's. No way of knowing this until after you buy them. The Cyclones tucked up above the frame rails, and had tubes more equal, how's that? The Hedmans hung down very low and were poorly engineered. There was at least 2" of clearance from the head pipes to the crossmember. No reason for that. I was seriously disgusted with the Hedmans- they weren't even bent correctly and I later found they hit my steering box and didn't allow the flange to sit square on the head. I drove the car around the block and the first time I cracked it open the gasket blew out and the 800° gases seered my valve cover, plug wires and melted my temp sender wire. I told Summit to eat the things. What a hassle. My car sat on jacks for another 3 weeks while my old headers were blasted, welded and HPC coated.
Another thing to consider when buying headers is find a set with separate flanges for each tube where it bolts to the head. This makes it easier to bolt them on. Hedman uses one solid flange. bad for mounting and bad for spark plug clearance. Hedman Hedders SUCK!
Well Scott we don't like to engage in vendor bashing. Everyone has their own opinion of good and bad. Headman sells more than one style or type of header for that matter and your car might not be sitting at stock ride height as determined by the Fisher Body manual (did you know some folks actually lower their cars? It reduces ground clearance for no good reason).
one other quick question ive also been told i would maybe have to swap over to a hydraulic cluch because the headers run right where the clucks linkage and stuff sits now ? anyone heard or ran into a problem? theres headers on the 327 thats in it now an i understand that the primaries will be alot bigger
The cross-shaft (Z-bar) on the big Impala is the same from big block to small block as the motor is not moved around in the engine bay to make room for things like a steering box like it is on the smaller cars. The headers should clear if the foot note states it will work with a manual transmission.