Poor some diesel into each of the spark plug holes, you will probably find that only two cylinders are seized. Refit the spark plugs and leave sealed up for two weeks and then remove the spark plugs and find out which of the cylinders are seized. Two of them should be still full up with diesel unless of course its seeped past the rings. A couple of squirts of oil down the other bores from an oil can won't hurt the engine.
Spinning the engine presuming that the engine has its boss for inserting the starting handle you should be able to fit it and stand on it. If you can't do that the crankshaft pulley should have a nice big nut on it that you can do something similar with with a big set of stilisons or an adjustable spanner.
I won't tell you how long it took me to turn my engine over but I wasn't in any hurry