Hi ThinkRob
I have a SL55 pump, oem fuelfilter, 665 cc/3,8 bar/55,1 psi/92 % duty cycle.
No problem at all. ( BUT i have a AutronicSM4 thats controls the fuel )
I think you will bee fine on oem fuelfilter and SL55 pump and 550 cc fuel injectors.
Dont use a adjustable fuel pressure regulator. You dont need it. Oem fuel filter is 3,8 bar/55,1 psi
If it is time concuming for the Tuner. Change tuner. They dont know what there doing

Regards Göran