As far back as the 60's and 70's cars came from the factory with crossovers, especially performance versions, because it aids low end torque, which is what's needed for the street. You would sacrifice this eliminating the crossover.
As far as "true Dual" exhaust, with or without the crossover, if you have seperate routes for exhaust on each side of the car from exhaust port to tail pipe it IS true dual. This is as opposed the having both sides of the engine exit into one pipe, go through the same catalytic converter, and then split into two mufflers and tail pipes, or go through the same muffler and then have two tail pipes.
Headers will improve performance and sound. Your catalytic converters are killing a lot of it though too. I think headers (long tube as you youngin's call them

) and straight flow through mufflers should amp up the volume.
Gotta remember, even in the commercial for the chambered mufflers they demonstrate them on an old Chevelle with no converters. :coolsmiley:
Steve