The turbo occupies a very particular place in 3 dimensional space. Even if you install an adapter flange, you will then need to find some way to line up the air outlet, oil inlet, oil outlet and exhaust pipe. Then there's the question of how the big turbo will perform with the smaller motor. None of this is impossible, but it would probably be cheaper to rebuild the T25 than to deal with all the resulting issues.

Let's back up a minute and ask what you mean by "toast". Maybe there's a way to bring it back from the brink.