I have used the 2.6.32-r51 kernel, no problems. I am not sure if you need to use the '_' vs '-' in the name.

The best way to work in the kernel (I have found) is to build the kernel and make sure it boots and things work on your SD card with the rootfs.
Then make your changes in tmp/work/overo.../linux-2.6.32-r51/git
Do a bitbake linux-omap3-2.6.32 -c compile -f, then bitbake linux-omap3-2.6.32 -c deploy. Copy the new kernel to the SD card and away you go.

For the SPI, the drivers are in the kernel. You will have to modify the board file in ..../git/arch/arm/mach=omap2/board-overo.c. You have to add the platform data structure for the SPI to expose the SPI drivers and system to the user as /dev/spi-dev

Search for spi dev in the mailing list and you should find a patch file.

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