Curious what kind of exhaust hangers you are using too? With our old trucks I have found that with any exhaust system, quality hangars designed to help insulate and allow the system to flex helps a lot (not solid mount with exhaust grommets alone). Terminating any exhaust out at the rear bumper helps reduce noise and to keep fumes out of vehicle. I run a stock 292 in a K10 with stock style exhaust system this way and it's very quiet on the interior, so much so that I hear gear whine more than anything. My Thread below with pics:
http://67-72chevytrucks.com/vboard/s...d.php?t=836212