This can happen when a brand new engine is not broken in yet and get overheated too much.
I have seen you previous post about your break in and saw the one with running too rich.
My brother have had this happen too him with the 454 also.
The engine is just too damn tight in the beginning. He got up to about 240 or over very fast and the engine just seized and would not budge. That you saw metal shavings is not good but nothing you can do about now.
Perhaps you temp gun is showing a bit off too.
Lets say you got to 230 but you are actually at 250 or so... not a bad thing on an engine already broken in but on these tight one it becomes a problem.

(just to comfort you, my brother and I broke 5 belts on two starter boxes breaking in two 454's)