H- or X-pipe on side exhaust

I know the benefit of using an H- or X-pipe in an exhaust system; however, is the benefit achieved only with a full exhaust system? I know the science of using the exhaust pulses to better scavenge the exhaust pipes, but will that matter on a shorter system?

My plan is to have side exhaust (from a somewhat warmer than stock 440) in a '68 'Cuda fastback. I want the pipes to exit just forward of the rear tires, such as with an AAR 'Cuda. I plan on using "header" mufflers bolted to the collectors.