Siezed 273 v/8

You should always be careful when trying to start up a motor that has sit for a long time and then won't turn over.

I have heard horror stories of mice or rats getting into the cylinder through the exhaust or intake manifold and then dieing thus rotting inside the motor causing it to freeze up.

Don't want to sound like I'm raining on your parade. Sorry, but I would crack open the heads and do the visual check. Could actually save you money in the long run.

Good luck...