First I would check that the pump is truly dead, these pumps are really very reliable and outlast the life of the car in most cases.
I don't know the ECU control system on the 4/4 as well as the +8 of the same era, but the fuel pump feed is controlled by the ECU, once up to fuel line pressure the ECU shuts off the supply. This might be an issue.
Secondly the most common problem for the fuel pump is a poor relay, which does not allow current to the pump , however with a separate feed I think we could rule this one out.
If you really do need to replace the pump I understand there are 2 methods but I only have experience of the first:-
1 Drop the whole fuel tank under the car. This is done by releasing the chassis bolts to the wooden mounting boards and then twisting each board carefully so that they can be removed, and the tank released downwards . Not an easy job for the home mechanic as you need quite a lot of clearance under the car , and the bolts holding the boards to the chassis , and the tank to the boards can be very messy to undo , and access is not easy at the best of times. You will also need to support the tank carefully as it is released.
2 I have been informed that it is possible to release the spare wheel mounting woodwork and gain access that way . As I have said I don't have any experience of this , and I can only envisage that access is going to be a major issue , and also whether the woodwork has been glued or bolted into place . I hope others who have tackled this will be along to comment soon.
Good luck
