Fuel pump choices?

You have just proved the point. Big engine, but low rpm. It will require less fuel than it would use at higher rpm. Hence small pump, lines etc because they are big enough to do the job. If we assume 4000 rpm max for this 534 ci engine, it will need about 25 gph @ 4000. That is using 70% as the VE at peak rpm [ 4000 ].