would I need (internal diameter, I mean) for an aftermarket fuel pressure regulator that is bolting on in place of the stock one?

 

Why? Just get a rising rate FPR and hook up to return line. My Stock regulator has inevitably gone out over the years. My aftermarket FPR works alone to regulate my fuel. It's Stillen and I've ran it for close to 8 years, no problems. I even left the guage installed so I can read my fuel pressure while under the hood. It hooks up to your vacuum line.

 

You dont bolt an aftermarket fpr into that stock spot.

You need a fitting that gets attached to the fuel rail, sx7r sells them, and then hook a hose to that and then mount the FPR in the engine bay somewhere.

http://forums.maxima.org/showthread....=stand+fitting

-matt