How many miles are there on the engine? Have you WD40 all the piston bores first and let it soak for a few days before putting a breaker bar on the crank and tried to move it? You may be lucky and find it releases easy, who knows until you try. If it does turn over easy then give it a kick and see how it runs for awhile,. I have had engine that felt locked before and once you get them turning over again would still be good. Of course sometimes they are not, but in my mind, why spend the money until you work out which way it goes?