Anything is possible, but the water pump is a very unlikely suspect. You can eliminate that possibility by removing the fan belt. Another long shot would be a broken tooth on a timing gear getting wedged into the other gear teeth, but it should be possible to dislodge that kind of a jam by turning the engine backwards with a pry bar on the flywheel teeth or an energetic shove toward the rear by a couple of beefy helpers. Pretend the front fenders are a blocking sled and recruit a couple of NFL linemen to help you out! (or maybe a couple of the ladies who hang out at a biker bar!)
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!