Chosen Solution

So I bought a iPhone 6s for 300 but when I got home it was Icloud locked. I have a iPhone 6s plus laying around that has a broken screen but the motheboard is in great condition. I wanted to see if I can take out the motherboard from the 6s plus and put it in the iPhone 6s.

No, won’t fit at all.

Likely not, the logic board also contains internal information that is incredibly difficult to change that tells the hardware whether it is a 6s or a plus. The information tells what type of drivers to load depending on model. For example, the screens are different sizes, the cameras are different, and the battery sizes are different.