Thank you very much for your feedback!
Please, what is the special treatment required for a mainline based kernel? Is there any existing documentation on this anywhere that I can refer to? My objective is kernel development, so getting mainline kernel working, along with the necessary debug tools and kernel headers is a strong requirement.
I did follow the instructions on the download page up until the last section on modifying the overlay, and as I could not get the kernel to boot, I was unable to make the change. Is there a method of making the changes to the image directly before attempting to boot?
Again, thank you very much in advance for all your help!