71 R.B. (Rust Bucket) gt /6 ?'s

By "blew the valve cover off" do you mean to say that the valve cover is shredded and the flange is still bolted to the head? If that is the case then yes I do know a way how that can happen.

Gas flooded engine, remove the spark plugs in an attempt to clear cylinders, very long matchstick to ignite and burn fuel in cylinders. This is the point where the fact that the spark plug tubes don't seal without plugs installed comes into the play. The fuel vapor will build up in the valve cover and that is where it will ignite violently. I still have the dented push-on style oil fill cap from when I learned this lesson when I was 18. If it had a twist on oil cap instead I don't know where all the force would have gone.

A picture would be nice.