Thats a good point about the cltuch vs the throw out bearing supplier. The final specification would HAVE to come from the throw out bearing manufacturer because only HE knows what style your using!
If it's made in China, all bets are off.
Twin disc is a different animal all right. Depth of the input shaft is critical, for instance. The trans throw out bearing collar may even need to be modified by grinding away a portion of it external base to allow for more travel of the throw out bearing.
Some throw out bearings do use a bearing assembly just like a front wheel bearing, tapered roller bearings. Other use ball bearings. It should be obvious which style you could run zero clearance with, or not.