Radley pull the plugs squirt some penatrating oil into each cylinder, let sit. Next day repeat. Try turning the engine over by the crack pulley. If it doesn't move try more penitrating oil and time.
Was there any oil in the crankcase (oilpan)? If not you will want to add some oil to the crankcase. Now one of the other members may have some suggestions but I would just use regular oil.
You may also want to pull the rocker arm shafts from the head and disasemble and clean then reassemble.
If you don't rush things you should be able to free up this engine. But don't be suprized if it dosn't run or runs poorly once you get it free.
Good luck to you and keep us posted with your progress!
