That sounds like the illustration in the BL GT6 Mk3 parts catalog. It's a little sketchy with the variations for the US emissions-spec Mk3's, since there were a few incarnations.
If you've never seen one of the distributors w/ vacuum advance & vacuum retard:
That photo is from a Clymer shop manual, which also has a very good exploded diagram of that distributor. It is probably the book I grab first for minor adjustment & repair operations (the factory shop manual reprint is far larger). It's a good manual, & you should grab one if you see it.
When my first one began to get ratty I got a new one, but the new one (fourth edition) has only 238 pages vs. the 1st edition's 327. One of the things missing in the 4th edition is that photo. Possibly they dropped it because they couldn't reconcile the line about "all Mk2's, +'s, & Mk3's had Delco distributors" with that distributor (obviously Lucas vacuum module design). Also they seem confused in the manual, which refers to that picture as GT6, GT6+, & TR250 distributor, but the exploded diagram labels it TR6.
I had a diagram somewhere of where the vacuum hoses were connected in the emissions-spec cars, but I can't find it now. One of the keys to the variations in setup, though, is the location of the carbon cannister: on the firewall or at the front of the engine.
I notice the original post is from almost 2 years ago. I suspect he got it sorted out or has given up by now.