It is easy I just did mine on a 2001 rodeo sport,try
www.isuzuparts.com for OEM I could not find after market.
Spray flange bolts well in advance with liquid wrench or Kroil to make removal easier,the old bolts can be tough,I normally change the tailpipe if it is as rusted as the muffler it makes for an easier and better job,don't forget to order gaskets,they are not common,but the link above stocks them.
Also look at the rubber hagers for damage,good luck.SF