If you used the u-boot install script it should have saved the original somewhere in the original 32Mb root filesystem.
Look at the environment variables to see where it tries to pick it up if there are no external boot devices present.
You should have something like this if external storage fails:
bootcmd_pogo=fsload uboot-original-mtd0.kwb; go 0x800200
This should pick up the original boot loader and execute it from ram in order to boot the original OS.
fsload will look in all the jffs2 filesystems in internal flash for a file called uboot-original-mtd0.kwb in the root of each filesystem.
Have a look on your system if it still boots something and see if you can recover your own version :-)