For some reason, 16K UFS block size is not possible with the original Gentoo kernel. Solution: Simply change linux-2.4.19-gentoo-r7/fs/ufs/super.c or similar according to the patch enclosed.
Created attachment 2307 [details] Patch to kernel fs/ufs/super.c file adding 16KB block size option
looking fs/ufs/super.c in 2.4.20 seems that as long as the blocksize is 4096 or more and is a power of 2, it is valid. so, 4096, 8192, 16384, etc,... are valid. therefore, this is no longer an issue in 2.4.20.