Ok after much trial and error I got it:
1st try:
Wanted to go back to the adding the kernels in the right order again just in case I missed something. Booted lts and installed zen, reboot. zen booted up. Installed cacule, reboot, zen booted up. Later I found that I missed adding the cacule-headers so I don't know if this had anything to do with this method not working but I moved on to 2nd try.
2nd try:
Modified /etc/default/grub and that booted up cacule but it got stuck on bootup screen. Alt+F4 to get out to terminal, installed the cacule-headers, reboot and now it selects the cacule kernel and boots fine.
Note: I guess the only tricky part is that the list starts from 0 so if you count as a human, cacule is the 5th choice down but in the GRUB_DEFAULT option, 4 works fine. Just making a note of it in case someone else reads this and tries to update their grub but it boots to the wrong one. I know that's just the way computers 'think' so no biggie.
Thanks, we can call it Solved/Work around for now 