"Will start and run if timed near TDC but is flat; wont start if timed before TDC."
This sounds like there is no mechanical or vacuum advance occurring.
iirc the Consuls, Zephyrs and Zodiacs used the Lucas 25D distributor, they are reliable once sorted but fiddling fingers and bad maintenance often causes problems.
Have a read of this:
http://simonlacey.com/pages_new/content/documents/lucastuning.pdf.
You should check that you have the correct cam, bob weights and springs fitted if you can find the original spec (often in the old Haynes and Auto books). Check that the end of the cam arm has not been filed away to increase maximum advance and that you have both a strong and a weak spring fitted, look for signs of the springs being bent in an attempt to change their effect.
The cam should be free to rotate on the drive shaft (limited by the springs etc) I suspect that yours is rusted in place or that the wrong screw or washer is fitted in the end of the shaft...under the rotor arm. I have seen one dizzy where this washer had broken and got jammed between the drive spindle and the points cam.
Once the mechanical advance is working, check the vacuum advance....suck on the vac. inlet and the spring should pull into the vac tank body. Check that the two parts of the points base plate are free to turn...the wrong screw in the condenser can lock them together.
Check the timing mark is correct, I cant remember if these have a bolt-on one or cast-in but put a screwdriver etc down No1 plug hole and slowly turn the engine
forwards until the piston is right at the top of the stroke, check that the timing marks line up.
Points gap is 15 thou. (this sets the dwell time, the duration the points are closed for)
Set the static timing to around 8 deg BTDC or what ever the manual says, only ever turn the engine forwards to the marks, if you overshoot turn back well before the marks and go forwards again. Hold the rotor arm backwards to take up any back-lash as you turn the dizzy body to the points break point. It should now start easily.
Use your strobe to check on the dizzi operation, first with vacuum disconnected, as you increase rpm you should see it advance smoothly to around 20 deg BTDC at high rpm. (static plus the advance as stamped on the cam arm).
Then at idle, connect one end of the vac pipe and suck on the other end, the timing should advance smoothly with increasing 'suck', it is often jerky due to the base plate not rotating freely.
Hope you get it sorted.
I have owned MkII Zephyr 6 Low Line, Mk III Zephyr 6 and a MkIII Police Special 6 with three brass SU carbs and a fancy 3 branch exhaust manifold.