Post the specifications of your engine. What carb, intake, heads, and cam are you running?
One of the biggest mistakes people make is oversizing their exhaust. Your exhaust needs to be tuned to your engines air flow capability. A 3" dual exhaust with stock heads is going to decrease performance.
If your basically stock, I'd go with 2" pipes, increase the pipe size depending on how warmed up your engine is.
This system is always for sale on Ebay. It comes with an H-pipe to fit the Tri-y headers or stock manifolds or HiPo manifolds, depending on which one you want. It does not give pipe size but says it will work with the GT extensions. All aluminized with turbo mufflers. They have a phone number listed that you can call if you have questions.
We are thinking of putting it on my sister's 65 Fastback with Tri-ys since he claims it fits good and it is priced fairly cheap, $139.00.
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