I'd go 8. You don't save a tremendous amount of gas with the 6, if you keep your foot out of the 8. It is a bolt-in using the proper original type equipment. 8s are more punchy, just feel like they wanna go, you'll have more HP and they do sound great with dual exhaust out the back..maybe flowmasters. You can also get more carb using the 8 (more cylinders to handle it) and get a nice vacuum secondary 4b, more power to run PS, or AC down the road. I just think the 8 is a better driver day to day.
If you are just just going to show it, then get the wildest thing you can stuff between the fenders, it won't matter much in terms of driveability.
