Jim L,
I wouldn't try to guess at what would cause it. Could be dirt ( If the engine has never been worked on before.) or maybe wrong Plunger Cylinder. The reason I say that is because I found two stuck in my engine and the engine had been rebuilt before I got it. The engine had sat for so long that some of the springs for the Plunger Cylinder had no spring left in them. I don't know maybe someone else would know if there were different sizes of Hyd. Lifters from other engines and when someone would look at them they looked close enough to work, but didn't and that's why you have one stuck and one loose (or maybe it's just worn out from lack of oil).
Just food for thought.
Also be careful not to crack the block.
Wes

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Jim L.
If memory servers me correctly, those lifters are hand made and paired up as they are being made. So if someone swapped any of the inner parts that would be a good reason the lifter got stuck. I looked last night but couldn't find where someone else had the same problem and made a clamp and was able to remove his stuck lifter. I hope somebody can point us to that topic.
Good luck.
Wes

Hi Jim L.
A few of us has been down that road, check out my link, I was able to get one out but not the other.
https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=9397&viewmode=flat&order=ASC&type=&mode=0&start=0
Also some body else had made a clamp that fit on the guide and was able to remove it from the engine, if I see it again I will post for you.
Wes

Thanks Dell, yes I will have to open it up one day and report back. For now this is a good reason not to have an electric pump feeding to a mechanical fuel pump and also if the electric fuel pump is install in the feed line to the carburetor between the mechanical fuel pump and carburetor then a one way valve should be installed keeping fuel from going to the mechanical fuel pump.
My two cents.
Wes

Hi, I smelled gas one day after starting up my Packard and look what I found. A leak from the fuel pump. Good reason not to have an electrical pump before a mechanical fuel pump.
See video at youtube:https://www.youtube.com/watch?v=UE27jspjpkU
Wes

The reason the "1" looks like an "I" is because old typewriters did have a "1" because they were suppose to use "I" for the number one.
Wes

Here's another, use an Engine Hoist with a dolly under the engine.
https://www.youtube.com/watch?v=uCVlNR8jdsA
Wes

Sorry about that last one here's a better video.
https://www.youtube.com/watch?v=YWxcQHPsdN4
Wes

Engine stand! We don't need NO stinking engine stand!
https://www.youtube.com/watch?v=G7EE9Dug9-M

Or was that badges?
Wes

Sorry I can't help, but I did see some Youtube videos of engines running on stands, maybe that might help.
Wes