The PI manifold should be the same. I know the one that came off my Vic motor is although I can't use it because its got warping under the tstat housing. The Vic/Marquis/Towncar intakes have a foam padded box around them that is not on the Mustang intakes and would need to come off.
Also be aware that the coolant tubes on the Vic/variants and the Mustang are not the same because of that stupid box the lower part of the intake sits in.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.