this looks to be an easy fix
https://squarebirds.org/Electrical/CVR/SolidStateRetrofit/
here are instructions but with a different regulator voltage for mgb
http://www.britishv8.org/Articles/Voltage-Regulator.htm
information here on different regulators
http://www.learnerswings.com/2014/07/5v-fixed-output-voltage-regulator-using.html