I see you've already got a Facet replacement, but if you still have the SU pump, they are simple to overhaul (so simple even I managed it) so that may be worth doing so you have a spare. Burlen Fuel Systems in Salisbury sell overhaul kits - you'll need two for a double pump.
SU Fuel Pumps & Spares - SU Carburetters
My 410 (a late 1969 car) also has the pump in the boot, but I don't know if it was originally there or not. It was comprehensively restored in the early 1990s.