There were a handful of Right Hand Drive 73-91 squarebody trucks made for UK standard roads in South Africa, Australia, New Zealand, etc. There are even a few that were imported back into North America in the last 30 to 40 years.
This is why I always use LH & RH in my descriptions and not driver/passenger sides.
Industry standard nomenclature for Left and Right hand sides of a vehicle... you'll find these used in the service manuals.
- LH is the seated driver's Left hand.
- RH is the seated drivers' Right hand.
Are you positive that all six of the rubber feed and return lines on the valve are routed to the proper steel feed and return lines?
Are you positive the LH fuel pump is the one that's running and not the RH pump?
You can check this at the two position fuel sender/pump disconnect to the LH sender using a test lamp. It should light for 2 seconds or so when you turn the ignition to ON.