Clean the heck out of every surface you normally can't reach. Install the passenger-side header at the engine. Wiggle the driver-side header into position but don't attach it yet. Bolt the starter in. Check out that mangled old thing next to the shiny new Summit piece.
Clearances are tight.
Thread the long driver-side insulator bolt back in. It may be necessary to slightly raise the engine to get it aligned right. Bolt up the driver-side header to the engine. Reattach the starter's wiring. Thread the long passenger-side insulator back in.