Siezed 273 v/8

Put marvel mystrey oil in the cylinders and let it sit.
Make sure when you squirt some in each cylinder that what ever your using sprays it sideways ,so that the oil hits the cylinder wall towards the inside of the motor.It will then coat the hole ring in the cylinder.
Use a breaker bar after you have let it sit a few days.
I worked on a pontiac 400 that was seized up and it worked.
GOOD LUCK:cheers:
PS iF YOU GET IT RUNNING, THEN USE A FULL QUART IN THE OIL, AFTER YOUR OIL CHANGE.