Someone was asking about the size of the radiator bleed bolt earlier, so I
thought I would mention what I did recently.  I made a  fitting to measure
the radiator pressure.  I took a brass nut (5/16") and drilled out the
center threads so the 8 mm radiator bolt would easy fit through it.  Then I
drilled an 1/8" hole sideways through one of the nut's flats into the
center hole.  I  then soldered 1/8" copper tubing to this hole in the side
of the nut.  Pinch this nut between the stock copper gasket and another
gasket.  I made a special bleed bolt from a 8mm x 1.25 bolt.  I drilled up
through the center of the bolt and then sideways to where the brass fitting
would line up.  You could accomplish the same thing by grooving the bolt up
the side.  Your stock bolt may work as is, if it is grooved this way.  To
the copper tubing I connected a vacuum/pressure gauge and pinched it under
the passenger side wiper blade.  This enables you to see the gauge while
driving.  I don't know if it would be robust enough to use this fitting as
a permanent installation, but it has held up very well.  I have since lent
it to a friend who was troubleshooting his coolant system.   There is a
flange above this bolt and not  very much room for anything much thicker
than this type of fitting.  It is also a good way to pressure check your
system.  You can quickly tell how tight your system is  by how soon the
pressure drops off once the engine is shut down.  A bleed valve could
conceivably be attached to this line also, if you did a more permanent
install.  I never saw any measurable vacuum at the radiator.  I would
suggest using a 0-30 psi gauge, as 0-15 psi is cutting it pretty close.  My
friend said he saw his pressure peg the gauge which was a 30" Hg (full
vacuum) to 15 psig gauge.

                                                                  Jay