Any recommendations for a dual exhaust and header combination for my K-code?

 

First, are you sure you want to modify your K code? They're valuable cars in stock form, so any modifications are almost sure to reduce the value if you need to sell it. If you do decide to go this route, DO NOT SELL YOUR HI-PO MANIFOLDS!!!! Don't sell anything original to the car, but definitely not those. Keep them somewhere safe in case you need to sell the car in the future.

Ideally, I'd recommend a set of Ford Powertrain (FPA) headers. They're expensive, but they're very nice. They tuck up under the car like nothing I've ever seen. Most pics I've seen show the collectors above the frame rails. If you don't want to go that route, a set of tri-y headers was all Shelby used on the GT350's. They work well and they're affordable.

Behind the headers, 2-1/4" pipe with an H-pipe as close to the collectors as possible and mufflers of your choosing.

 

Like Starfury said, you want to keep all the original components to your K-Code because of it's value.
I would definitely go with some Ceramic Coated Tri-Y headers, They fit well and are snug under the car and are not obnoxious. All you need to go on that car is with 2 1/4" inch exhaust with an H-Pipe and some nice Dynomax Super Turbos or Magnaflow mufflers and tailpipes all the way to the rear. You don't want anything loud like Flowmasters, but you still want it to sound good.

 

I don't know about the super turbos. I had some on my car for a while. They sounded good at idle and under load at low rpm's, but they were almost inaudible while cruising and sounded tinny above 3k rpm.

 

My grandfather picked up the K-code at a swap meet for me. I do not have a K-code original car (regrettably). I am putting it in my 66 coupe that is not original by any means. I figured I would swap out the old straight six to give me a little more motivation to insure it and drive it more often. I appreciate your advise.

 

If it's a complete K code motor, I'd sell it to someone restoring a K code car and use the proceeds to buy another motor. My $0.02.

 

Exactly....assuming it's a real K code motor. Take the valve covers off and see if there are pockets for the valve springs cast into the heads.

 

Or a VIN stamped on the block right above the oil pan. It's more valuable to a K car and owner. It's easier to get the same hp from modern technology on a 'plain' V8 today.