[hEaT]

The lines in the second picture are for the DPFE/EGR system. I'm not sure which line has which, but I know that they are modified by that black box.

As it has been determined, the line in the 3rd picture is a fuel line. Not going to help you unless you are doing a fuel pressure gauge.

The lines in the 1st and 2nd pictures are related to the DPFE/EGR system and do not have reliable vacuum readings.

I just took a quick look at my 01 and it seems the line that comes out of the middle of the rear of the intake manifold looks the best. It's the only standard sized line and it seems to snake through the intake runners. It looks like it's spliced together in one section where you would be able to separate the lines, add the T, and then reconnect. I'd would just double check and see where the lines goes and make sure it's nothing that is critical where a slightly different vacuum reading would impede the engine. Also, make sure to seal the NPT fitting on the back of the gauge with teflon tape. If not, it will leak.

BTW, are you boosted or planning to? If not, the vacuum gauge won't tell you anything really unless you are trying to diagnose a problem.