This is the stuff   you really need !!!!!

There is two sheets of it on E-bay

http://cgi.ebay.com/INCONEL-SHEET-HAYNES-230-061-065-X-36-00-X-38-750-/250607109439?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item3a5959053f

http://cgi.ebay.com/INCONEL-SHEET-HAYNES-230-061-065-X-48-00-X-38-750-/250607111834?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item3a59590e9a


Plenty to make a couple of mufflers.

BTW here is the stats for HAYNES  230 inconel

http://www.hightempmetals.com/techdata/hitempHaynes230data.php

Tony