it's those split washers that are your problem. When they are in original condition they can be all mangled up and just make installation a nightmare. Take a wire wheel to them. Also you can soak them in CLR (Calcium, Lime Rust) solvent. Works great. Best option would be have them soda blasted like Luis did. Paint them with high temp paint or leave them as is. The most important thing is that they are not majorly deformed or bent. It makes installation a nightmare. Also, the big ring can be installed both ways. Make sure you have those oriented correctly. Last installation I used the help of my growing son, and ratchet straps as my split washers are mangled up. I had to modify one of them. If you can start the nuts on both sides, the header can be seated with the nuts safely.