I'm not familiar with E1-R2... but if it's anything like a PRI or ISDN trunk, try change inc-call-handling-trmt trunk-group XX. If you are on an older switch, do cha isdn inc instead.
This lets you adjust numbers coming inward and convert them.
Going the outward you will need to take a look at UDP/AAR/Route-patterns to change your DNIS to the far end.