Actually, csh and tcsh are one and the same on FreeBSD. /bin/csh is a hard link to /bin/tcsh (Check the inode).
Back to the original question, If you want zsh as root, but don't want to change the default shell, you can do is just start
zsh by typing it after you used
su to become root.
As for your history search command, as far as I know csh isn't able to do exactly that.
csh does have a more or less similar option called
autoexpand. If you type
ls it and press
up, it will only show you the commands that start with
ls.
IMHO tcsh is a fairly usable interactive shell, but many people are put off by the not-always-equally-sane default options.
Here is what I use, and would personally consider a slightly more sane cshrc:
http://rwxrwxrwx.net/csh.cshrc
Save it as /root/.cshrc overwrite the file that is already there.