If the breather element is left intact at the DS cam cover the pcv system is no longer functional as your pulling unmetered air into the engine.(which can cause a lean condition)
On a centri and turbo setup pcv is forgotten by most. From idle to 3000rpm the car is N/A and vacuum is present . Above 3000 your making boost through the intake and with a stock Marauder pcv valve (which isn't intended for boost) it will allow the boost pressure to enter the PS cam cover.
The post Blazed71 put up is good but I would make a few changes to it as newer and better parts are now available.
1) no need to gut the OEM pcv or swap the inlet for the pcv location to the DS cam cover. (03 cobras have a push in pcv valve)
)2 Get a pcv valve for a 2008-2010 GT500 it will screw into the stock location no problem with one exception. Its too tall. So cut it down to length with a hack saw
3)add a one way check valve at the stock location on the intake (yes you can keep your catch can if that's what you want to call it
)
This setup will yield a cleaner look and will out perform Embassy's old setup. If you want to get fancy you could get a wiring pig tail and wire the heater element for fun. The Gt500 pcv has one built in
I have no doubts you were sending boost into the engine as you have presented it.
Research the 8 rib swap, and if a 3 bolt cover isn't in your future at least get a single bolt thumprr tensioner.. They're expensive but well worth it!!
Sorry for the interruptions...… Please carry on……..