Was the car running OK before components were replaced? If so I would check that the filter/regulator and pump connections are all as they should be, it's easy to cross them and it really doesn't work well then........ If it is all working correctly you shouldn't need to be putting NRV's in the system or modifying it, it's not perfect but it does work OK. If your friend doesn't have the Walbro fuel pump fitted to his M3W, he should do. Full instructions are available in the owners resources at the top of this forum.
I am trying to think how quick the fuel pressure drops off after turning off. I never timed it but it was a visible fall of the gauge, so not that long, maybe a minute or so? I wouldn't say that 40 seconds was a big issue as long as you are getting a steady 58psi when the pump is running. All the injectors need is a steady head of pressure.
