My car was doing exactly the same thing.
Engine would cut out during low speed aggressive braking.
I also have a fairly wild cam fitted.
I made up an Alloy vacuum bottle of about 2 litres capacity with an in & out fitting.
Vacuum line from engine to an Earls check valve, (one way) before the bottle.
Then a short hose from the bottle to the brake booster.
Vacuum bottle is mounted in front of the booster.
Problem solved, never had the engine cut out since.
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