Ford Repair: Starter wont rotate motor, ford f 150, plug holes

Question
Hi Steve,

I have a problem with my 1977 Ford F-150 4x4, 400 motor, auto transmission.  The motor got hot and woudnt restart. I thought it was the starter selenoid/relay so replaced it, no good. Replaced battery, no good. then replaced starter, still no good. After investigating, I found that the starter was not even budging the flexplate, so no rotate.  I tryed turning the  motor by hand with a breaker bar on the dampner bolt and it wont budge. Motor Seized??
Was running great before this happened, but teen age boys can work wonders.  
do you have any suggestions or tricks to possably get to motor un seized.  I am going to try taking spark plugs out and put some Marvel Mystery oil in the cylinders but thats about all the ideas I have.
Any help would be greatly appreciated.
Thanx

Answer
Mark-

  It certainly sounds like your motor is seized.  You know you're in trouble if you can't turn it with a breaker bar.  Your best betright now would be to pour some Marvel's or plain old diesel fuel into the spark plug holes and let it sit for a while...preferably overnight.  If you still can't break it loose, it may be a lost cause.  If it does come free just do an oil change immediately and then start to assess the damage, if any.  Hope this helps.

Steve