I found this site whilst browsing....
http://members.aol.com/IDICPage/main.html It shows the big differences between the TOS D6 Klingon battlecruiser and the later D7 battlecruiser models used for filming.
The TOS D6 and the TMP D7 battlecruisers are intended to NOT be the same class of ship, as some mistakenly believe that the TOS Klingon battlecruiser is a D7 and not the D6. It was always a D6 back in the 1960's, 1970's and 1980's in canon and fanon. I think it was FASA who started the TOS D7 "myth" and it sort of took off.
Also, underside details and decals (yes there were decals!!) on various piece of the hull of the TOS 11 Foot Enterprise. These were panel labels.
There is a list of what the panel labels are on the hull, and what they say.
Needless to say, all Model Please's TOS Constitutions will have all the panels marked accordingly, just for accuracy's sake and absolute perfection.
Also the engines on the TOS Romulan Warbird that everyone thinks has a ball front end, are based on the 1975 Aurora model kit, which did the engines wrong. The pictures of the actual TOS model show them as being different.
Anyhow, the site is a modeller's bonanza, especially for those fanatical about detail.