Just went through this and wanted to ad what I had to do. I ended up snapping one of the bolts off of the flange. I spent the better part of the day soaking it with PB blaster and trying to wrench it out. I could not get it out. After taking the exhaust manifold off and trying with no luck, I took the hammer too it. Two whacks and it popped out. I have a 95, and apparently these bolts are not threaded in but have grooves. No matter how much you wrench it, it won't come out. It needs to be drove out like a pin. Hope this helps someone else out.