Hi Tim,
As someone who just finished clearing up a green pool, I can tell you that the SLAM process will work. At first, you will need to test your FC level more often (every hour or so). Keep bringing the FC level back up to your shock level, which is 20 ppm, based on a CYA level of 50. It is important to do this often, in the beginning, so the algae does not have a chance to take over. You can use the PoolMath tool to figure out how much bleach to add. I found it to be a useful tool for this process.
Obviously, this can be hard because you need to have enough time to do this, depending on your schedule. I was able to test early in the morning, and add whatever bleach I need to add to get it to shock level. Then, after work at night, I was able to test 4-5 times before bed time, adding bleach as needed. Weekends worked out much better because I could SLAM the pool all day, during the sunlight hours when your FC level will likely go down the most.
Good luck!