Those are numbers from the Japanese numbering system, or Asian numbers if you prefer. As opposed to the "American" numbers like 2N4401 or MPSA06. And then ther is the Euro system numbers like BC550.
When you see those A or C (or B or D) numbers, there is a 2S understood at the start of the number. SO you have a 2SC3198 and a 2SA1266. That might make searching for them easier. Catalogs and data books will always use the full number. On the parts themselves they don;t waste the space to print the 2S. Some makers use a K instead of 2S, so you may see KC3198
Small TO92 asian types have the pinout left to right facing the flat side as E-C-B. AMerican types have the leg order E-B-C. And for the life of me I can never remember the order on the Euro types, I have to look it up every time. I don't use them very often.
You can replace one type with another of different leg order if the specs are similar, you just have to turn the transistor sideways so the legs can be positioned over the correct holes.
My records show the 2SC3198 as a 60v 150ma NPN, and since the noise figuer is listed in the quick guide, I have to assume it is a lower noise part. The 2SA1266 is a 50v 150ma PNP, also lower in noise. Not to say a regular plain old transistor won;t have low enough noise for you, it may work just fine.
I know I keep a drawer full of 2SC3198 for some purpose, forget what now. Mackie maybe? Behringer? SOmething I fix uses them. Doesn;t help you any, I know.