In a way, it’s great that you get many lines and then get stuck. This means that you have successfully copied the “compatible” kernel file.
However, you didn’t follow the instructions closely enough. You MUST touch the /Library/Extensions folder. At reboot time, this signals to the kernel that it should invalidate the kernel extensions (kext) caches, and rebuild them.
Because you skipped this step, you’ve got a mismatch now between the recently replaced (older) kernel, and the kext caches. That’s why it’s stopping.
”How did that happen?” I hear you ask. Well... when you allowed the Apple update to install, it did both things, it installed the incompatible (newer) kernel, and it invalidated and rebuilt the caches. They were rebuilt using the newer incompatible kernel as their base.
When you “downgrade” to the older kernel, you have to do the same, invalidate the caches and get them to rebuild using the older kernel as their base.
Boot from your Recovery HD, from the Utilities menu launch the Terminal. Using the Terminal command line issue the touch command. If I Assume your El Capitan partition is called “Macintosh HD” (alter this to suit if it is not)...
Code:
touch “/Volumes/Macintosh HD/Library/Extensions”
And for safe measure let’s do the System Extensions too
Code:
touch “/Volumes/Macintosh HD/System/Library/Extensions”
From the
menu, choose Restart, use CMD+v to see the boot text it should give you an indication of what it’s doing. Hopefully you will see it invalidating the caches and rebuilding them. Fingers crossed it should proceed to the login screen (eventually. We’re talking minutes not hours though).
Be patient, it might take a short time to rebuild the caches....