Having been there, done that, I don't think you're gonna like the undercar rumble you'll get with terminating the pipes under the car right after the mufflers. It resonates through all the sheet metal of the car and makes it miserable to drive after a while.

Also, unless you're runnin' a 600 hp big block, there's no reason you'll need 3" pipes. I know it's all the rage, but it'll do you no good if you have just a street-type small block. As a matter of fact, you'll probably see more low-end torque from the motor with some reasonably sized piping like 2 1/4". No matter what anyone says to the contrary, a motor needs a little bit of back pressure to operate properly. When NHRA racers were forced to put mufflers on their Super class cars, they found out much to their surprise that the cars went faster and quicker with the little bit of back pressure afforded by the mufflers as opposed to straight out the collectors. 3" pipes will be a mis-match in your combination, like I said, unless your making 600 hp.

I can't recommend one muffler over the other because I only use glasspacks. If you were to run 2 1/4" pipes through a couple of shorty glasspacks and to the outside of the car, I think you'd have all the noise you could stand. Run a 2" H or X pipe between the pipes after the collectors and before the mufflers.

I don't know the specs on your "mild racing cam", but unless you chose a cam to operate with your static compression ratio, you may find that the car is slower since the cam change due to a soggier bottom end.