I am not sure what others will say but I would recommend the long tube headers and 3" exhaust but I am bias because that is what I now run and it sounds awesome.
347 with long tubes w/3" x-pipe and 3" 1 chamber flowmasters with turndowns.
As for size I would say go with the 1 3/4" and you should make up the loss in low-end torque with high-end horsepower, that’s even if you loose any torque.
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James Cox
nochevy@hotmail.com
1991 Mustang LX
12.565 @109.38mph 1.764 60ft