Well, the former President of GOClubGP had that setup on his GP GT, and with an otherwise stock motor, managed a mid-13. You might want to get rid of your resonator in favor of a straight pipe.
As far as a good intake, you may want to take a look at this:
There'* a lot of info there. As far as being able to handle boost, I believe they have stood up to 13psi before. Make sure to get yourself some aluminum LIM gaskets, though.
Also, did your trans upgrade include all the different parts from the HD trans? If not, then it won't live long under boost.
Finally, no body kits for the GP will work on the Bonnie. Completely different car, totally different platform. It'* sister car is the LeSabre, and it'* closely related to the Park Avenue, Riviera, and Aurora.
Basically it'* as closely related to the Grand Prix as the Crown Vic is to the Mustang. Same motor, different car.
EDIT: If you have seirous concerns about the upper intake, You could replace the whole thing with a UIM/LIM from an F-body. I know it'* been done on GPs, not sure if it will fit under the hood of the Bonnie. Of course, it would involve a lot of work, as it puts the TB on the passenger side of the motor.
EDIT MORE: You might be able to get the body cladding from a GXP, which is a lot smoother, and more flowing. The tails also got rid of the black grid and the indents in the signals.