it 425 engine interchangeability??

I just acquired my first dirt bike. Its an '80 it425. The problem is that it looks as though the chain failed sometime in the bikes life, and it took out part of the engine casing over the clutch pivot on the left side case. Finding a suitable replacement is proving difficult. :bang:

Are there any other models that use the same cases as this one?

Any help would be great.

Shaun