I have a FT-1000MP (plain) and I just installed the IF mod. I can tell you it is worth it. I spent countless hours researching all the mods for the MP on the internet.
Here is a great link that will explain it better and advise you on a "test" that will allow you to decide if it will work for you.http://lists.contesting.com/_yaesu/1998-05/msg00099.html
If you operate CW the K9AN CW audio mod is good to.
Check out my posts on the Yahoo FT-1000 users groups.