I know it's a long shot, but if anyone will be in the area...I'm going there to do some exploring either this Friday or Sunday.
Here's a guide to the roads there
http://tpwd.texas.gov/publications/pwdpubs/media/pwd_bk_p4501_0152k.pdf
I've been out there a bunch. It's amazing - I'm sure you'll have a great weekend. Just a heads up, the trails in the state park are not well marked. That PDF you posted is quite helpful though. The whole place is incredibly remote. Nothing too challenging from an off roading standpoint, but well worth the trip for the stunning scenery. I'm curious to see how the trails have changed since all the rain we've had in TX this year. I'd love to see pics if you take any.
Checkout the Starlight Theater in Terlingua for dinner if you have time. Try to catch a sunset from their front porch - you won't forget it.
Anyway, have a great trip, travel safe.
**EDIT** I just looked up where brewster county was - I now realize I probably didn't tell you anything you didn't already know. haha, my bad.