The pressure in the fuel rail measured relative to atmospheric will vary, it tracks the pressure in the plenum. According to the Rover EFI reference it should be around 2.5 bar (37 psi) above plenum. I checked my +8 a week ago and at idle the pressure is 30 psi, and at fast idle with throttle open it is 35 psi, so maybe a bit low. I am currently running on the standard regulator I don't have a reference standard for pressure so did check the fuel pressure gauge against three other gauges and they all corresponded, just hope that are not all faulty with exactly the same error.
The original external fuel pump was said to be a Lucas 4FP / Rover PRC6242, I am also on the hunt for a replacement. Ideally I would like one with a filter on the inlet to take out any large debris, Facit make some but I haven't found a high pressure version. Failing that an in line filter may be the answer, but it has to be a high flow (coarse) filter so as not to cause an undue restriction. A concern is that there is a lot of relatively cheap pumps around and its difficult to be sure of the quality. I did buy a cheap pump some years ago to carry around as a spare and get me back home, but a pump stopping on a motorway, or when pulling out of a junction, is something to be avoided.
The technical sheets show that with vacuum disconnected to regulator the priming pressure should be 40psi which in turn will provide around 34psi running pressure when vacuum reconnected.
