Fuel pressure regulator plumbing : 850 Demon with a Carter mech. pump

You should get a diagnostic fuel pressure gage and secure to the windsheild. Make a few full power runs and see what the presure's doing. I know enough about Demons that I frankly avoid them - they are very sensitive to atmospheric and fuel pressure. Overly so IMO. If the car does not slow down every time - I don't feel it's worth revamping the fuel system until you have proof there's an issue.