Slant fuel pump securing screws?

[GTS290N]

The fuel pump oil leak has been getting steadily worse, so whilst the car is off-road awaiting brake parts to arrive I thought I would fit a new pump to block gasket, from one of the 9 now available to me!
Both bolts securing the fuel pump were loose.
Pump off, old gasket (nowt wrong with it) off and surfaces cleaned, new gasket, pump on.
Looking at the parts book the screws/bolts only have a flat washer on the securing screws, any reason why I shouldn't fit a spring washer?

[xvivalve]

They may make it harder to get the correct alignment of the pump lever on the cam...

[AlanH]

Use the 'magnet in socket' method.