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If the rings are stuck into the piston grooves - I doubt you're ever going to get free without pulling it apart. That being said - if it stuck in that way - it would still have compression - since the rings were against the cylinder walls when it first GOT stuck. It will be low, but it won't be zero.
I've never found an engine with stuck rings that had zero compression once some oil was added. Pour some light oil into the spark-plug holes and crank it. If the compression does NOT come up - I doubt your rings are the problem. It may just be your valves - regardless if they're stuck or not. I've fixed many Hercules flatheads like that. The valve-seat is just cast-iron tends to get a layer of rust and debris on it. Then, even with valve moving up and down, there's no sealing and no compression. Since it's so easy to pull the head - seems you ought to take it off and take a look. I had to fix two flatheads recently - an IXB Hercules and a F162 Continental. Both had sat in storage for years, both had zero compression, and both had the valves moving up and down - but not sealing at all. I had to cut the seats pretty deep with a carbide cutter - but they ran like new when done.
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