11mm zexel pump head(M51 is 10mm) from Nissan patrol y61 2,8 td6 (RD28ETi). Theoretically gives 21% more fuel at all conditions.
New from BOSCH/ZEXEL is stupidly cheap(around 100 Euro retail price).
Would make no difference. The injection pump has an internal capacity that cannot be exceeded. Providing there is enough basic fuel feed flow, what goes through the injection pump is determined by fuel injected and fuel returned via a flow return restrictor. Flow through the injection pump cannot be increased by uprated lift pump flow rate.