They are filled and assembled without the spring, I will get - hopefully - rubber cups from McMaster to use as the "condom" on them.
I set them up in vice, adjust to hardest setting (shortest spring) and used zip ties all around to keep the spring down - not really safe method but it worked. After that I was able to slip out the end big ring that holds the spring on.
To put the spring back on I will have to figure out some spring compressor, maybe just adapter to a big clamp or something, but that's later.