The way I play has the Urbie set up as more of a "point-man" in a dedicated urban combat oriented light lance, taking the punishment and dishing it back out.
LBX-AC/10 with two tons of ammo, as you do. Two heat sinks removed to give space for the extra ton of ammo and to add a Clan ER Small Laser for some PD. Maybe add an extra ton of armor for some protection.
I usually run this in a lance with a WLF-1B, a PNT-9R, and a RVN-3L. Wolfhound and Panther are my heavy hitters, Urbie's the point-man (as I've already explained), and Raven's the scout.
Sometimes I switch out the Raven for an Owens for some long range missile goodness, but the Raven is usually the better option for urban combat.