Hi JG -
I see you're still wrangling your brakes from your your previous thread about upgrading your hydraulics. Let's take it from square one:
First, I agree with Biff - a pressure bleeder cures a lot of brake bleeding ills and takes a bunch of guesswork out of the equation. So let's look at the equation we have now:
You've rebuilt or replaced most of the major components ao we know that there was air in the system big time after the replacement.
Did you Bench Bleed the rebuilt master cylinder?
Have you checked all rigid and flexible lines for pinholes, dents, crimps, dry rot/cracking of rubber lines?
You mentioned in the last thread that you ordered a new flexible line - did that improve the situation at all?
Checked all wheel cylinders and calipers ( If Applicable) visually for leakage?
If all these things have been done, the bakes are adjusted correctly and all else appears copacetic then that point to either air in the system or a bad Master Cylinder, for whatever reason.
My opinion of the dual reservoir dual purpose master brake/clutch cylinder is this: tho it's quaint, charming and a wonderful example of how somebody engineered a single component to do 2 jobs It seems to me that it is sorta complex for what it's supposed to do - If it was such a great system why did they abandon it so early in the model evolution in favor of a much simpler, less expensive and trouble free units such as the ones that they used for quite a while after this dubious engineering masterpiece?
My suggestion: If you've done everything correctly as you outlined in your posts and the thing still doesn't work, don't keep flogging a dead horse - replace the old cylinder with a new or factory rebuilt exchange unit - preferrably on of the newer single function units which are available from not only the british supply houses but can be found very inexpensively at places like AutoZone, PepBoys and Advance Auto.
You may have to modify the pedal box a bit but it sounds like you're no stranger to modifying stuff as witnessed by your description of your car in your previous thread. After all, all the cylinder has to do is forced hydraulic fluid through a line to another cylinder - it really doesn't matter how it looks or what year car it's supposed to fit as long as it pushes the juice, eh?
Good Luck Chap!