RE: bolt size on exhaust bracket?
Are these for the muffler interconnect bracket? If it is, there are two bolts each that connect the mufflers to the interconnect bracket. You have to get underneath to get to the heads.
If these are the bolts you are looking for, then they are 5/16-18 x 3/4.
As far as the exhaust system goes, these are the only 5/16 bolts. The rest are 3/8.
I got this info from my parts book for a 2006 Sportster. It should be the same for a 2005 I imagine. I hope that helps.
If it is a different bolt, let me know and maybe I can find it. If not, pull that sucker out and go to a hardware store and try to match up.
As to anti-seize -- I am not sure I'd use anti-seize on those. I usually use blue loctite on my bolts. I'd rather take time getting them off, than having them vibrate off somewhere on the highway.