Please note, I am only a lay person and still learning so the following information might not be acurate;
The main meditation practice in Tendai is Maka Shikan, which originates from Tientai (Chinese) and is believed to be the forerunner to Chan (Zen). Here is a book which outlines the practice http://www.amazon.co.uk/Essentials-Budd ... 52&sr=8-11
I'm afraid I don't know of a free copy.
There are other practices which are also utilised such as contemplation, visualisation and mantra. Please see here for contemplation practice. http://dctendai.blogspot.com/2010/07/ho ... ation.html
I'm not sure how (or if) meditation is classified in Tendai. Tendai is vast. All ordained members of the sangha have experience in most, if not, all areas of practice. However, because of the sheer size of Tendai, the average priest cannot master them all. Some choose mikkyo (mantras & rituals), some choose kaihogyo, some choose nembutsu and some choose meditation. I would guess to say that all these practices are "pillars" as Tendai views them as equal paths to enlightenment.
Some one like Jikan might have a more knowledgable answer.