A common misconception is that the pump controls pressure. It DOES NOT. The pressure regulator is part of the fuel distributor in K-jet and K-jet w/lambda. The KE cars have an external separate fuel pressure regulator.
The only way the pump can affect this pressure is if it doesn't pump enough to be regulated.
There are a couple differences in pumps that could make a difference. The pumps have an internal by-pass (safety valve) to keep them from blowing up if the system is plugged. Since the systems work at different pressures the blow-off pressures will be different which could mess things up if say a pump used on an EFI systems (running 45psi or less) were used on a K-jet at 70psi or a KE-jet running 90psi. I think the blow-off pressure would be set high enough that a K-jet pump probably could be used on the higher pressure KE systems (not that I would recommend it).
The other factor in pump design is volume. Different pumps do produce different flow rates. Not as much fuel is needed to mantain pressure on a 4cyl as opposed to an 8cyl. The factor of safety in design here is probably large enough that a 4cyl KE pump would probably do good enough for a 8cyl but why take it to the edge.
The proper test for fuel pumps is volume at pressure. This is easy to measure by taking the return line off the fuel pressure reg. This fuel would be returning to the tank. The fuel in the system is regulated and the excess is what you measure.
Bosch Master, ASE Master, L1
33 years MB technician