It is not easy to find film footage of Master Tang to study his moves. Moreover, they are all in black and white. However, it is the basic info that is more important than the aesthetics.
The following link is a forehand jump smash 2 step style from the base position to the deep forehand position. Notice the immense power of the right foot (for left handed players vice versa) to push the body weight off the ground in 1 step. Also the shoes being worn then were probably something that resembles the china 'dragonfly' brand.
Another moving rally. Notice how his centre of gravity is slightly forward when pushing forward. You can see his movements are lightning fast although it's only still pictures. All shots are taken as high as possible.
This is the Xiong Guo Bao's link for you. For badminton newcomers who really interested to improve their backhand technique. Here, Xiong says it is the face held in such a way during the backhand where your palm faces outward. However it is the face of the racket that is facing you, that is hit, and not the face of the racket that is facing outward. This means, if the hand is your racket, it is the opposite site of your palm (the knuckle side) that hits the shuttle.
You can see from this video that Xiong literally tires his opponent who is hitting to his backhand using a forehand. Now, how can a backhand be less tiring than a forehand? It is all in his technique. Watch and learn.
In the era of 15 points system, Xiong Guo Bao was once touted as the backhand king who could tire his opponent's forehand! One of the reasons both fans and sports enthusiasts alike can instantly think of such a mastery is because there are really few who master the backhand perfectly. This also due to the indoctrination that it is best not to use the backhand at all, if possible. So when we see one that purposely use the backhand to an advantage, it is so easy to single out the very few of them. Morten Frost has a good backhand, mind you, just that he would rather not use it. Yang Yang's backhand is no fluke either, blasting a backhand cross court smash that caused Morten Frost to tumble to the floor diving in the final minutes of the 3rd set. Xiong Guo Bao's backhand smash has been seen many times during his heydays. This unorthodox method of delivery which has a skill mastery to inflict a smash are by standards, very few.
In the era of 21points system, Taufik comes to mind. LCW's backhand clear is flawless and looks simply easy. But very seldom do they attempt a smash from a full baseline position.
Guo Bao's revolutionary grip (only his rackets have it) resonates Tang Xianhu's method of playing with concentration on and utilization of your fingers.