Different mounting system to accomodate the fact that the new one's engine can move independantly of the frame, and also a crossover between the mufflers on the new ones, rather than too f'in close to the idle mix screw on the old ones.
That's one of many reasons I love my V&H Straightshots on my 99 - no crossover. Sure, if I'd dyno it, I'm sure the machine could detect a small flat spot due to not taking advantage of the reversion created by the crossover, but I'm not a racer, and my ass-dyno just isn't that sensitive. But now I can get to the mixture screw without burning the **** out of my hands!
Klouse