How Could I Be So Stupid/Careless?

In 1982 I was adjusting the timing on my 70 Duster with a T/A 340 and had the 8" air cleaner just sitting on top of the carburetor with the nut loose on the dished cover. I moved the timing a bit then reached down to give it a rev, when the engine backfired and the air cleaner jumped off, the nut went straight up, hit the bottom of the hood, then went directly in the carb and got sucked into the intake and right into a cylinder. All I heard was a crunch and the engine died and white smoke coming out of the drivers side pipe. Took the head off and a valve was sitting sideways in a piston. Here is a pic in 1981 with the soon to be wife I am still married to, in better times of course...

70 Duster 1982.jpg