There are many places which describe bits and pieces of the history of these cars but Paul Williams has done a very nice job of assembling the bits and pieces into a nice concise history. Paul writes for Canadian Driver and another one called Driven. Bits and pieces of Paul's original article (1995) from this website (sometimes without proper credit!) have made their way onto lots of other wedge sites so don't be surprised if some of the content looks familiar. Now you know who wrote it!
Another site really worth visiting is the Unofficial AustinRover Web Resource. There is an entire Triumph section (click on Triumph in the MARQUES section on the left hand side of the webpage) with several whole "chapters" (with photos) devoted to The Shape (written by Keith Adams). There's a lot of stuff there and it really expands on what Paul originally wrote. Well worth browsing!