That seems odd. Even before that book came out, the first omnimech was always stated to be inspired by the modular weapon mounts on the mercury, and in the book the Coyotl was said to be the logical extension of Star League research. Seems odd they wouldn't ask you to make it look like the original Mercury.
The mercury II is from one of the Jihad books as a Wolverine mech. In universe, the other clans hate everything wolverine.
Whatever the case, this art is fairly good (though I prefer the other omnis from that book). Looks very much like an originating design, solid, but unrefined just like the tech that goes into it.
If i may help out: the principle of OMNI-Mechs, the modularity that makes them so flexibly, not the mech itself, was inspired by the mercury´s weapon mounts. And the first omni was created by the Coyotes!