I don't think he intends to control the pulse width with the SU, he will leave the pump to alter its pulse rate to suite the fuel delivery he sets on the control valve, much like the carburettor ona car. Using the SU pump keeps it simple and easy to understand.
Incidently as someone who did his apprenticship on Austin and the BMC cars I would not agree the pumps were as unreliable a syou imply, but certainly more unreliable than the AC mechanical pumps. However a swift whack with a spanner usually sorted them until you had a chnace to clean and adjust the contacts.