I just did the job for a NA 3.8. It wasn't too bad, but still involved lots of dissassembly to get to those gaskets. Unfortunately there are big differences in the actual details of the procedure for the 3.1 and 3.4 liter engines. The best write up I have found is here .

You will need a complete gasket set. Gaskets from a better parts store like Carquest / NAPA will have an improved design like the ones here.

Good luck.