Kirk,
I have used pumps like the one in this ad on several Tractions.
I bought the last one about 10 years ago and my online search back then found a number of similar pumps readily available on the US.

It is fitted to my 15/6 and, although it is perfectly capable of running the car on it’s own, I generally only use it to prime the system when it has been stood for more than just a couple of days. It also proved invaluable when we experienced vapour lock in very hot conditions on the way to the Polish ICCCR.
I have it fitted in series with, and just before, the mechanical pump. Power is taken from the ignition switch via an overide switch on the dash.

B…..