Just installed Thorley ceramic coated 'long' headers and an Edlebrock intake manifold to go under a 750cfm Edlebrock Carb on my '78 440. WOW!! Don't know the gas mileage yet, but it can easily pick up speed going uphill.
Let us know the gas mileage when you find out. Also would be interested in the before gas mileage.
Were the headers coated both inside and outside?
Thanks for the info
I called Thorley about the coating. They are chrome plated but not ceramic coated. They do not make ceramic coated headers. You can get them ceramic coated for about $300 from other vendors. However, they 'guaranteed' me that these headers will run cooler than the stock manifolds. They cost me $498. They were fairly easy to install and when installed there is more room between the headers and the side of the doghouse opening than the original manifolds. I did have to remove the starter and loosen the large nut on the passenger side motor mount to raise the motor a couple inches. Also, these headers are a couple feet longer than the original manifolds so be prepared for additional exhaust work.