Get summitracing 1103 cam and lifter kit, any brand of longtube headers 1 5/8, and true dual exhaust and your rocking. I have a cousin with a 67 gmc and it has this set up on his 350 and it sounds nice. Runs pretty good to,but i think gears will make it even meaner along the line of 342 or 355.
P.S. my mousie 305 with 700r and 342 gears eats my cousins 67 350 turbo400 3:08 gear for breakfast. POint being. Im a fan of rear end gears