Read the Manual!
It would be fair to say that I wouldn't be able to get too far without some reliable owner manuals
The three manuals that I've used throughout the project are the Haynes Owners Workshop Manual, the original Owner's Handbook and the Shop Manual. The Owner's Handbooks are actually quite rare now, so it's good to have got my hands on one of these.
I'd also like to find some original promotional materials, brochures or advertisement prints. So if you know of where I can get any of these please let me know.