While not quite as clean as tanking them this didn't take very long (after removing the covers) and anything left will be finished off with a few short OCI with Mobil 1 0w-40. No problems in over 100K after this was done, oil consumption, further deposits.Before/after (front head). I had a machine shop hot tank the head.
I don’t think any amount of chemicals will clean the sludge you showed. If you want to fully clean it, you will need to have the valvetrain hot tanked.