I was going to ask the same question for my 460 powered truck.

 

Headers for a highboy pretty much don't exist last I checked. You can't use 2wd headers and headers for a half ton don't fit either. Last one I did because like you I couldn't take the noise anymore. I did 2.5 from the stock manifolds into a X pipe then I did a flowmaster 70 series dual inlet and went out with 3inch and a flowmaster hush resonator and exited behind drivers tire. It fit the bill for what I wanted, word of warning it was so quiet I often thought it stalled while in traffic.

 

When I put the rebuilt 400 back in my truck I went with new headers (I believe Hedmans) because both of the stock manifolds were cracked. The headers were actually cheaper than the repop manifolds and breathe better. Added some Dynomax mufflers that are relatively quiet but have a nice tone. You have to make sure you get the correct headers for your front end to have the proper clearance. The truck sounds good with no leaks. My truck is a 78 F250 4x4.

 

 

Flowmaster Super 44's, They growl off open throttle,, but not overly obnoxious after you open the throttle.

 

Personally I would keep the duals... just need a quieter muffler and manifolds that don't leak.. A generic stock replacement muffler similar size or bigger to what you have would quiet it down a bunch. Or a turbo muffler which is pretty quiet cruising and has some bellow when you get on it.

Adding an H pipe to connect both sides of the duals near the front will also quiet id down some and also improve performance.

 

 

Just ordered Sanderson ff 427 and x pipe from summitt minutes ago. Hoping to use powerstick mufflers and have shop run the pipes at 2.5". Wish me luck as I might need new starter.

 

 

Longer dual in/ single out magnaflow muffler. Like 24" long. 2-1/4" dual in, 3" single out.

 

I was in your boat. Just took ownership of my dad's '77 Highboy and literally the day I got it, the tail pipe fell off from rot. Being in the Denver metro area, emissions are required on '76 and newer, they wouldn't even test it with the missing tail pipe.

I went to a local shop and had them custom fit a true dual system from the manifolds back, using Flowmaster Series 40's and I absolutely LOVE those cans. I get compliments and thumbs up literally every time I drive it. No, it's definitely not quiet, but certainly not obnoxious by any means. Very healthy rumble at idle, and surprisingly quiet and drone free at highway speeds. If needed, I'd put the exact same system back on. Cost was $450 total, which you can't beat.

As for headers, I found nothing after market, except for Headman's, but heard numerous negative reviews about them. Everything from fitment issues, to warping issues, to rusting issues. The deciding factor tho was that there was very little proof that they even help boost performance. But, I'm running a 351M which from what I know isn't a very tunable motor, so take it for what it is....

 

I agree on keeping the duals, better flow and better sound. Adding an X pipe (or at minimum an H pipe) is even better.

 

There are some available.

 

Fenderwell exits are the only headers I would ever consider running, I have had to pull one too many headers just for a simple starter replacement, and it's no fun! lol