Absolutely first thing you need to do is get a wideband. That will tell you if in fact you are gettin lean misfire - which I highly doubt as you're running a 12:1 already. It might be running sluggishly lean compared to MBT mixture, but it shouldn't misfire.

The fuel pressure regulator is designed to keep a constant relative pressure compared to intake manifold pressure. You check the base fuel pressure by unplugging your vacuum reference, and say it reads 50psi. When you plug your reference hose back up (say you have 20"Hg vacuum on your manifold) your fuel pressure will drop ~10psi (Hg->psi conversion) in order to keep your relative pressure between the two equal. That's the reasoning for a 1:1 rising rate FPR. It accounts for vacuum, but also raises the pressure 1psi per 1lb of boost, to keep that same ratio.

Quick questions, what year is your car and ECU that you're using? Some early ECU's don't require missing link/FCD. How is your FMU hooked up (location, plumbing)? Are you using the stock FPR now?

Personally I'd junk the 190 and get a 255 Walbro, you'll need it eventually anyway.

Good starting place

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'95 GS w/ t3/t4b
FMIC, diy piping & RFL BOV
MS2-Extra Fuel&Spark
50 lb/hr Holley injectors w/ 1:1 RRFPR
JE 8.8:1 dish w/ Hastings Rings
Eagle Rods w/ ARP bolts
ARP Head studs
Mild port/polish head
3" custom DP/cat section, 3" PIT catback
dual MBC - 12 psi / 20psi