I'm glad you decided to try the surgery yourself. It's not complicated, and you won't even need to use sutures to close the incision. Here are instructions on how to do the surgery.
http://www.the-chicken-chick.com/2014/06/chicken-anatomy-crop-impacted-crop-sour.html
Before you try the surgery, you might be able to soften the impaction with a combination of coconut oil and stool softener. I recently had a hen with a very serious impaction and this worked for her.
What I did was to give her the oil first, massaging her crop for five minutes each time. After three infusions of coconut oil and massages, I then gave her one stool softener capsule. I waited a bit and did more massaging. Finally the mass broke up and left the crop.
If this fails, then do the surgery. It's simple, easy and effective. I'm surprised the vet didn't do any of these things. You can do much better by your hen.