Now that's what I call an impressive stat block.
A tail slap for a Colossal+ dragon does 4d8, so maybe we could use that for its slam attack?
Suggested Skill Ranks: Bluff 69, Intimidate 69, Knowledge (Geography) 69, Knowledge (History) 69, Knowledge (Local) 69, Knowledge (Nature) 69, Knowledge (Religion) 69, Listen 69, Search 69, Sense Motive 69, Spot 69, Survival 69, Swim 69, Tumble 69
Suggested Feats: Ability Focus (poison), Awesome Blow, Blind-Fight, Cleave, Combat Expertise, Great Cleave, Improved Bull Rush, Improved Critical (bite), Improved Feint, Improved Initiative, Improved Overrun, Improved Sunder, Multiattack, Power Attack, Snatch, Track, Weapon Focus (bite).
Epic Feats: Epic Prowess, Epic Sunder, Devastating Critical (bite), Legendary Tracker, Overwhelming Critical (bite), Superior Initiative.
Alternates: Epic Reflexes, Lightning Reflexes.
CR of "comparable" epic dragons:
Ancient Force Dragon (65 HD) CR 43
Wyrm Force Dragon (70 HD) CR 50
Very old Prismatic Dragon (63 HD) CR 52
Ancient Prismatic Dragon (68 HD) CR 57