Here's Jim Widess holding mold-grown portrait gourd sculptures of himself.
The light-colored one is the gourd's natural color. The darker one was stained with dark tea.
Almost any object can be used as a pattern for gourd mold.
Most likely you'll want to cast your head full-sized and make a mold from that.
Watch this space for an instructable detailing that process.
The mold must be slightly smaller than the gourd's natural size.
Match the gourd to the rough size and shape of the object you're molding.
There are gourds that grow very large and in a variety of shapes.