Further up I saw someone had problems holding the headers on. I had similar issues holding my exhaust headers on my gas engines. Problem was solved by using Permatex Ultra Copper sealant on the bolts and flange and adding NordLoc washers on the bolt heads. The sealant is silicone high temp gas resistant material that takes one hell of alot of heat and stays flexible. Try it...

BTW if you guys need a better solution for flexible coupling material, let me recommend you do as follows: I discovered this solution a couple years ago and it is better than Teflon. I build my own couplers for gas exhaust using ceramic fabric impregnated with Permatex Ultra Copper. It is simply rolled on a suitable, teflon lined mandrel and secured tightly with teflon tape for a day to cure the Ultra Copper. I use 2-3 layers of fabric. These simply do not blow out. In addition if you need to make a bent coupler, it is simple to do precisely as long as you have a shaping mandrel to mold around