I don't think those kernels can be booted from a dedicated partition anymore. A standard file copy to the /boot directory of your Linux partition should do it. You'll need to create the file a1boot.conf (also lives in /boot) and use the standard Amiga multiboot method in U-Boot. A list of Linux configs should appear after the OS4 options.
An example a1boot.conf:
Sarge-2.4.26 /boot/kernel-2.4.26.img root=/dev/hdb2 video=radeon:1024x768-8@70 l2cr=0x80000000 ide=nodma
That's for the old 2.4.26 kernel, obviously. Arguments will be different on the newer ones.
It should be all one line. The syntax is
[config name] [path to kernel] [arguments]
And it really hasn't been made clear, but these new kernels might require a hardware-fixed A1 - the USB and IDE/Ethernet DMA corrections.
