MC fuel system questions

[james accordino]

I have an 89 200q with an MC-2 engine.  My metering
head is starting to leak fuel into the airbox.  I have
several complete fuel systems from MC-1 engines, and
would like to swap an entire "system" until I can
diagnose/repair the original.  Here's what I know. 
The warm-up valve, cold start valve and potentiometer
are all identical.  The frequency valve has a
different p/n, but I think this is because the MC-1
has a flare nut on the end of the attached fuel pipe
and the MC-2 has a banjo.  The MC-2 has an external
pressure regulator behind the airbox attached to the
pressure damper.  The MC-1 system does not.  The
metering heads have different p/n's.  I have 035 133
481M and 034 133 481C, CV and CX from MC-1's and mine
is an 034 133 481J.  Visually the externals of these
metering heads are all identical.  Is the pressure
regulator inside the metering head on these MC-1
heads?  The air plate also has different #'s.  The
MC-1's are either 034 133 471B or C, while my MC-2 is
an L.  Again no obvious physical differences.  My
questions are basically: Where is the pressure
regulator on the earlier models?  Is this a necessary
item?  Are there any "real" differences betweeen the
metering heads or air plates?

TIA
Jim Accordino