Bummer! Take the dust cover off the flywheel, and try to turn the engine backwards to its normal direction of rotation. Sometimes that will dislodge something that has wedged itself into a bearing. It would be a very good idea to drop the oil pan and check all the connecting rods for discoloration or lack of side play. Also look for evidence that the oil squirters above the troughs in the pan might be mis-aimed, causing oil starvation at speeds above idle. Has the engine had good oil pressure up until now? It's very unusual for an engine to just lock up without giving some warning first in the way of knocking or oil pressure loss.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!