2004 Rev 800h.o Header Bolts/plug Question

OKay guys and gals. I have a 2004 Ski-doo 800H.O Adrenaline. Boysen Reeds. I hit a jump landed pretty soft. Then stood on it up to 80mph in a trail. Then let off to wait for the everyone to catch up. Once I let off I heard a funny sound. I opened the side skirts to find oil all over the enging bay. I looked at the headers and yep I was missing 3 header bolts off the right side cylinder. I had no choice but to drive it home. About 15miles and I didn't go above 5thousand RPM. About 20mph. I pulled the plugs half way back and put new ones in. They where covered in burnt oil. Never really seen anything like it. My question is. If I put new header bolts back in. How tight do the header bolts go? Will the gasket be garbage now? Do I need a new header gasket? Can I use a bolt head from the hardware store or do I need the allen key head? Why are my plugs like that? Thanks for your help