Larry,
>Frame and engine numbers do match T120CDU7766 and as I have been unable to find any definitive list available
The numbers alone don't tell the story as machines were numbered sequentially irrespective of model. When Triumph closed down their records were deposited with the Science Museum in London but when they wanted to get rid of them a couple of years back they went to the VMCC. So the VMCC, where you started your queries, should have the answer you require.
Regards, Peter C.