Deman Motorspot -
http://www.demanmotorsport.com/demanmotorsport/ is across the river from you. I take my 964 to Advanced Automotive - (845) 562-0346 in Vails Gate, also close by across the river. The owner Tom is a great guy and owns a 964 (and a 944 Turbo race car for that matter). Rennwerke is in Elmsford - (914) 592 4006. I don't know anything about them, but they are PCA approved, as are the other two. Good luck!