INTERMITTENT IGNITION ISSUE

I had very similar issue in our 67 cuda. When mine died twice it was on the 401 hwy(6 lanes) at 110kmh. NOT fun doing an immediate 4-5 lane change with no juice.
Anyway, check ignition switch. Our wiring was in great shape, BUT its 50+ years old and showing its age with cracks etc.
Good luck, I parked mine for 4 years and wanted to hurl dog turds at it.