Yeah even though its for a YJ, it applies to FSJ's too.
Overall, I love it. Had it on the truck for nearly a decade now. I am assuming the one you have a 32/36 DGEV? This is the one I have.
If you have only the bare carb, and not the Jeep specific model, you will need a few things. There is an intake adapter, and there is a linkage adapter. You need both, and both are available from
http://www.carbs.net (They have a huge section for the Webers). They also have the jets intended for a 258. I lived at 4k ft and worked at 5ft for years, and it worked well for me. I have been as high as 6500ish with no major issues, but it was most likely a bit rich.
I also strongly suggest a fuel regulator. I ran without one for a LONG time. But I always had issues with a stumble at idle and running a bit rich. Turns out the stock pump was pushing fuel past the needle and seat. A regulator set to 3psi resolved these issues, and Weber specifically states that a regulator must be used. I just never figured how much the stock fuel pump puts out. Turns out it will hit 12psi. I also lowered the float, as the stock setting its pretty high and results in flooding out on inclines way too easily. With the float dropped a bit, its much better. Also if offroading, you can drop the fuel pressure down to 1.5psi and this helps prevent flooding out even more. But you may starve for fuel at WOT.
Also if need be, I have the full manual scanned in the event you do not have it. Tuning a Weber is very different from an Edelbrock or Holley. The DGEV Webers are basically two carbs grafted together. You have a low speed circuit, and a high speed circuit. This means you need to tune it in a specific manner. Which is not difficult at all, just different.
Back when my J10 had stock gears, no lift, and 31's, I could easily get 17mpg out on the freeway. Now I get way worse, but thats to be expected with my setup.