Sounds electrical - If the keypad is still there and the control box under the dash, I think the cheapest option would be to totally remove the Brant and put something else in.
Other than that, you basically start doing:
- Fuel Pump
- Coil Packs
- Spark Plugs
-
ECU
- Crank Angle Sensor
List goes on. The most likely culprit in my experience with Bugeyes, is the Brant if it has one installed.