Re: LIM Gasket
I did this recently on my '98 3.1L V6. You definitely want to replace the thermostat, since it is a real bear to get to without removing some of the parts that will be removed during the LIM replacement. Also,there is an O-ring seal that goes to the oil pump shaft that sits near the valley on the driver side of the engine. This is real easy to get to with the LIM removed. The gasket kit that I purchased included this gasket, so I used it.
Also, I would check all of the hoses and the serpentine belt. You're going to be removing/disconnecting these anyway, and it might make sense to replace them while you are there. When I pulled the fuel injectors/fuel rail out of its seat, several of the O-rings were in pretty bad shape. I had purchased replacement O-rings before I started this job, and I was glad I did. Otherwise, I would have had several down days waiting for these pieces to be delivered.
You should probably also have the gaskets for the EGR valve and the throttle body. Also, there is an O-ring that might get lost if you disconnect the fuel rail from the fuels lines. Some on the forum have just set/tied the fuel rail out of the way during this work to avoid breaking the fuel line connection.
There are quite a few posts on this job on this forum and on the web, that were extremely helpful when I was considering this job. Feel free to PM me if you have any questions. Good luck.