AFTER you get the piston un-stuck:
Buy a compression test gauge, Harbor Freight has them,
http://www.harborfreight.com/, their site is down right now but search on 'compression' and the gauge should show up.
Search this site for 'compression test' and there's probably lots of posts on how to do it and what you should see.
If the compression is below spec, get back to us.
Also, the carbs will need (probably) to be pulled and remove the 4 float bowls and if there's any crud inside, search this site for how to clean carbs and do that.
New engine oil and filter, probably new battery, new spark plugs.
Check the gas tank, if it's rusty and/or smells like varnish, you'll need to flush it and maybe use POR15 or Kream to seal it.
That'll get you started.