That's correct. There isn't enough hood clearance for both the TB spacer and the FIPK so you can have only one or the other unless you make a hole in the hood and stick a hood scoop on it.
I suggest you make your own FIPK and save yourself a bunch of $$$. You can copy the one I made (details on my website).
A header won't make a huge difference by itself. It's the front pipe that's restrictive so if you replace it with a better pipe (a muffler shop can make one for you) that doesn't have crimps and chushes in it, you'll gain most of the benefits of the header.
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1992 XJ Laredo with
4.6L I6 HO Stroker -
AX15,
NP231,
D35c,
D30
Best 1/4 mile [email protected] with 240hp/280lbft from modded 4.0L I6
Websites - Jeep 4.0 Performance,
4.6L Stroker Build-Up,
Dino's Jeep Tricks