Re: muffler gasket blowout
Dave, I'll repeat what I said above about the flatness of the exhaust flange. If it isn't flat and doesn't fit flush across the full face you'll blow gaskets. Also the metallic gasket, copper or aluminum, will leak if the flange isn't flat.
Try this: Remove and clean the flange of any gasket material or exhaust residue. Use a magic marker, machinist dye or a Sharpie and 'paint tha gasket surface. Now rub the flange against a flat surface such as glass with a sheet of medium grit, about 280 sandpaper on the glass. It only takes a swipe or two then look at the flange where you painted it with the ink. You'll quickly see where the high and low spots are and what needs to be done to make the flange gasket surface flat.
As for the fasteners coming loose, try replacing the nuts and studs with Allen head capscrews. Torque them to about 60 inch pounds then check the torque after a few heat/cool cycles. I think you'll cure your problems.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"