I JUST PUT IN NEW LONG TUBE HEADERS IN MY CHEVELLE, I HAD 2 TAKE OFF MY VALVE COVERS, STEERING COLUME,SPARK PLUGS OFF IN ORDER 2 FIT THE HEADERS IN RIGHT. I PUT EVERYTHING BACK AND MY CAR DOES NOT WANT 2 START. I HEAR A BIG CLUNK COMING OUT OF THE HEADERS. DOES ANY1 KNOW WHAT COULD BE WRONG
sorry about the caps...

I'd double check the firing order of the spark plug wires.

You missing any tools?