A pinup of the two of them would be amazing, would you really need a setting?
Some of the gearhead thing, I can understand. Part of Kayleigh's appeal on Firefly was the combination of her ball-of-sunshine personality and her affinity with Serenity.
On the slightly more unsettling side, apparently even animated female gearheads have quite the following. Witness Gadeget Hackwrench.
Yeah, that cult that worships Gadget is kind of creepy.
Drunken analyses by my friends have determined that a woman who becomes a gearhead increases her odds in the dating game by *at least* 20%. At least. We're not talking about women who are into cars simply because they're expensive, but rather women who enjoy them for their own sake.
A female friend of mine is very into motorcycles, and before she got her first one at nineteen her mother told her that she would be hurting her chances with the boys. It took her a while to realize, but eventually she discovered that her mother was very, very wrong.