OK, here's the after-action report.
30' '92 454 TBI 61 k miles, w/ 4L80E was getting 7.5 - 7.7 mpg solo at 65. Thorley headers ($420), Flowmaster 70 series 3" in and out ($99) used original cat and pipes, new Bosch plugs ($15), K&N ($35), dryer hose from aircleaner snout out to grill. 8 hours of nasty work (4 broken studs.) Thorley kit is excellent...everything fits. And it's not chrome, it's nickel.
Runs smoother, noise not an issue, more torque at
1500 rpms and up, 5 degrees less water temp, and 10.1 MPG. I know, I didn't believe it either. We went racing this weekend and ran 100 gallons through it coming and going. 10.1 mpg. Why anybody puts up with those stupid iron manifolds and burned plug wires is beyond me.