I wonder if the pumps we get here are quoted in imperial gallons or US gallons? That might account for the lower figures. The other reason may be that our cars generally had much smaller engines, so most pumps were not designed for supplying a 260 V8 engine!
Today I took off the hose after the filter, to check the delivery rate. Switched on, and watched the fuel piddle out pathetically, no wonder the engine was dying. But after half a minute, I noticed there were quite a few bubbles coming through, and then the pump started a different rhythm, slower and more purposeful, followed by good spurts of fuel. The can then filled up quite rapidly. So it seems like there was an air lock, which has now cleared. Fortunately there was no sign of black flakes or other detritus. So I will run the car again, and hopefully, that’s cured it. Thanks for you replies Barry.