oh come on, start looking in rules.ini yourself.
Then you'll see the key LargeVisceroid=VISC_LRG in the general section, which defines the unit that appears when 2 baby visceroids combine. So there is no chance at all, that 2 baby visc can create your new unit.
So just start adding your new unit and notice that it works. Even if it wouldn't have worked, it would still have been much faster than this question/answer game in this topic.

P.S.: make sure you use LargeVisceroid=yes, because with SmallVisceroid=yes can 2 of your new units combine to a large visceroid.
This post has been edited by Lin Kuei Ominae: Jun 20 2009, 07:47 AM