Which 100cc+ engine will fit on an aprilia sr50 or runner 50 frame?

Hello there! I got an aprilia sr50 02 frame and a gilera runner 01 frame and I am thinking about buying an engine which is 100cc-200cc for either of the frames.

My questions are:
A: Which engine/engines will fit in the aprilia frame?
B: Which engine/engines will fit in the runner frame?
C: Which would be the cheapest engine to buy for these frames?

Would really appreciate if someone could help me out here. Im from sweden and have been looking in swedish forums but cant find ****.

Also, excuse me if my English is bad obviously its not my native language .

Thanks!