it should not be any problem as long as you take it to a competent muffler shop....

here is the old link to what I did
http://www.xoutpost.com/x5-e53-forum/...usts-4-4i.html


here is a link to one being auctioned on ebay..



http://cgi.ebay.com/ebaymotors/BMW-X...spagenameZWDVW

..i think when bmw change to the N62 engine in 04 from the previous M62 engine they change the way the pipes aligned . so I just had to cut out a short portion and install a new one to make it fit .. If you like you can also add an X pipe if you want a louder sounding muffler which is what some of the members on this forum has done in the past .. good luck