Hey I got one just like that one, only it has three cylinders, saddlebags and a windshield, but it does say Triumph on the tank, and its about that dirty.
Nice find, BTW. I've got a late 60's something or other Triumph that I know absolutely nothing about. Before we were married someone owed my wife some money so he gave her this bike. It was running when it was parked, but someone before me took the points cover off of it, I have the cover. It still has all the original parts, as best as I can tell minus one side cover. And I have no idea what size engine or even the exact year. It is a one banger, its in my mom's basement where it has lived for 10 years since we were married. I'll try to get some pics and post them up.