How big's the motor? If it's a small block with less than 400 cubes, what Jet said. I run that same set up on my 351w Mustang except with an "H" pipe and get tons of compliments at every car show. Personally I think the "H" pipe sounds more old school muscle car then does the "X" pipe, but it's a matter of taste. If it's a big block or over 400 cubes, I'd use three inch tail pipes. That's what's going in my '64 Fairlane Sports Coupe when the 427w goes in.
sreno: what headers are those, Crites? You did an excellent job on that exhaust; what a night mare it must have been to get right!