just copy from git-1.4.2.ebuild and you're done. 1.4.2.1 contains bug fixes only. Tested on ~x86.
*git-1.4.2.1 (13 Sep 2006) 13 Sep 2006; Fernando J. Pereda <ferdy@gentoo.org> +git-1.4.2.1.ebuild: New upstream version.