I champion for GURPS as well. Yes, it's a pretty crunch heavy system but there is a defined Steampunk (and Screampunk) setting book to go with it and you can tailor it to suit anything you like.

Also, anything that does post-apoc would probably convert pretty quicksmart to steampunk. Just substitute a "working" society with a rigid class system for lawlessness and change the names of "Nuclear Car" to "Steam Engine".