There are different degrees of "stuck". Are you able to get any movement at all, or have you tried? Once it's on the stand, reattach the flywheel so you'll have something to pry on, and remove the cytlinder head. Scrape out any serious rust deposits above the pistons, then soak the cylinders with some type of penetrating oil such sa Diesel fuel, Marvel Mystery oil, Kroil, Liquid Wrench, or PB Blaster. WD-40 is a poor excuse for penetrating oil, so use it only if nothing else is available. After a few days of soaking, a pry bar on the flywheel teeth might allow you to move the engine a little. Keep working it until you can see where the pistons were stopped originally. If there are deep pits, it's time for a rebore or even sleeves. If the pits are very shallow, they can be honed out.

If soaking and prying won't break it loose, count on a total rebuild, or possibly scrap it and find another engine.
Jerry

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