Looking at some comparable (stone-like constructs) creatures:
Stone Colossus (Colossal): Str 70, Dex 5, Con -, Int -, Wis 10, Cha 1
Stone Golem, Greater (Large): Str 37, Dex 7, Con —, Int —, Wis 11, Cha 1
Juggernaut (Huge): Str 31, Dex 3, Con --, Int --, Wis 15, Cha 16
Death Hurler (Huge; from Dragon 309): Str 26, Dex 18, Con --, Int --, Wis 12, Cha 1
I'd say that Strength should be more in the 50-60 range, and Dexterity 3-7. Considering its a bridge, I'd vote for the low end of the Dex range. I think your mental stats are good.