I just tried to save a pullet, treating impacted crop for a month, that was going through same things you've described. First I wormed her, then treated as if sour crop, then realized it was impacted. We ALMOST saved her. She aspirated while expelling a large amount of liquid and then I could see a grass/straw mass in her throat. We kept pulling and pulling the straw and if only she'd been able to hang on a little longer, that was the issue. So the obstruction might not be worms.
But also, even though I'm sad that we lost her, she had wry tail and though crop problems and wry tail are not related, I did feel like genetically something was not right. And upon further thought about that. In nature a mother hen will decide to not let chicks that are "not right," live. But in hatcheries there is no chance for natural selection to cull out the bad genetics.... So I'm not happy that she died but I am glad that she's not dealing with a poor quality of life. She could not balance and walk right with that huge crop, not able to jump up to roost with her mates, etc. I feel like the issues were going to continue had she survived.
I'd do what you're doing, keep trying everything, but if she doesn't make it, it was probably for the best. Good Luck.