There are a total of four tensioners, including on that is under the AC compressor, but only two need to be released to do the IMS. You must pull the IMS to crankshaft tensioner, and the one on the cylinder head you have the cam locks. I would suggest your review the following link, as it discusses tensioner locations and what really needs to be removed to do a retrofit:
LN Engineering Retrofit Kit Instructions, rev 18 - 996 Series (Carrera, Carrera 4, Carrera 4S, Targa) - RennTech.org Forums