1998 v40 t4 Fuel Injector questions

[def420]

Hello all you fine Volvo Afficionados.

After quite the sparepart extravaganza on my 1998 V40 T4, im left with a issue regarding the Fuel Injectors and FPR.

First things first. How does one determine the right Fuel Injector?? Meaning that I have searched the original Siemens (the grey top ones) for my Volvo, and theres none to be had.
Now question is, wich ones do i buy instead? The blue ones, the red ones or another one?? Allso, i see that the nozzle end of these injectors, is not the same for all injectors. Does this matter??

Second: The FPR, whats up with this quite expensive piece of metal?? Does one really need it?? How does it function?? Is there any difference in the one for my car (V40 T4 1998 Ph1) and others?? I mean that the pressure on most of them is around 300 kPa, and the original one for the 1998 models is 307 kPa. Allso is there difference in the ones used in an opel loop fuel line, and closed loop ??



Sorry for rattling about :-] Just beeing a noob, with tons of questions.