You've got a good car there, and could leave it as is and be cool. But if it were me I'd install the 348, save the 6 to put back in if you sell it. The weight difference probly won't be that much, those 6's were pretty heavy. I'd put glasspacks under it, 2/3 the way back from the motor, and have the exhausts exit just ahead of the rear tires out the sides, crome tips maybe. I wouldn't shave unless you need to look presentable, but maybe have it lean foreword just a touch.