Just guessing, because I have spitz.
zImage-c7x0.bin can be renamed to zImage.bin, copied to card and then flashed using Sharp flashing utility. zImage-kexecboot-c7x0.bin can be booted from another kexec capable kernel (I am afraid that Sharp ROM cannot kexec). There are two versions. Each of them has probably different bugs.
For more try to search distro list and machine specific howtos.