Does anyone have any suggestions how I may unseize Falcon BA 2003 4litre engine?

why or how is it siezed? pull it out, drop the sump, pull the crank, pull the head, get a drift on the underside of the slug and give it a good thump with a lead hammer. one by one, it will unsieze.

you cant rotate the motor?

Its knackered mate, its cheaper to go to the wreckers and get another.

much easier to just get another engine mate, by the time you pull it out, pull it apart unseize the motor and put it back together you might aswell pull the motor out, and throw a wrecker engine in, not to mention if you just pull it apart fix whatever has seized it and put it back together its going to cause more problems, theres a big reason why the engine would stop turning