I did Macbeth about 4 years ago, and while I don't still have a cutting of the script, I can tell you at least some of what we cut.
The Ross/Old Man bit from Act 2 Scene 4
All of Act 3 Scene 5 (Hecate)
Some of Act 4 Scene 3. I cannot remember what off-hand, but it is a LONG scene. Some of the interaction between Macduff and Malcolm can be cut. We did cut the bit with the doctor in that scene.
I think we cut a good portion of Act 5 Scene 2.
I hope that helps. It won't quite get you down to 90 minutes, but it'd be a start.
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Christopher Hamilton
Drama Teacher
Kennewick WA
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