Thanks, Art - I think it's how I have this beast configured......
Al: Speedsters ended in 1958-59, replaced by Convertible "D" and then Roadsters - both different.
It appears, from this and from the pages that Tom posted as well as stuff on the 356 Registry, that the Speedster was only sold in America, imported through Max Hoffman, starting in 1954 and ending in 1958 (although a few left-overs were sold as 1959 models).
The two major shortfalls of the T-1&2 Speedster were it's seats and it's flimsy top, both of which were replaced on the Convertible D (built by Drauz, rather than by Reuters because Reuters was max'd out building coupes) with cabriolet seats, roll-up windows and a (more) decent top. Other than doors with windows and a taller windshield, the body of a "D" is supposedly the same as the other T-2 cars.
The Convertible "D" was a one-year-wonder and only 1330 were made in 1958, making them pretty rare, and carrying sales over into 1959, when they were tooling up for the "B" series, ending the T-2 and ending the speedster entirely after the "D" for the 356 B Roadster.
The "B" roadster was designated as a T-5, and later they added rear disk brakes to the T-6 to become a "C" model. Usually, changes in designation (T-5 to T-6, say) had a bunch of little details changing, but you get the idea. The 356 lasted until 1965 (I've heard that the last ten were cabriolets built as Police cars!) when it was replaced by the 911.
This is not a detailed summary by any means - for more detail, the 356 Registry is probably the best place to look.
That's all I know without going to look on the Registry.