[mrud]

I was having the exact same problem with my 427 so. I finally fount the culprit. What I did was purchase and electric fuel pressure gauge and permanently mounted it under my dash with a clock so it looked professional. Found out that when the car sat for over a week, fuel pressure would bleed down. When I crank the engine, it took quite awhile for fuel pressure to build back up and then the engine started. Problem: leaking down fuel pump.
Replaced, fuel pressure comes right up: engine starts. Let me know it that helps. BTW. If you plan on putting a fuel pressure gauge in your cabin like I did. Please, please and pay the extra $$ for an electric gauge with a sensor. You do not want a line running into your car with fuel as in mechanical gauge.
Regards,
Mike R