Yes it is possible. Keyboard from A1278 works fine on A1342, but! The light layer do it Fat, and that may be problem. the light layer powered on 14-18V and need to use additional Led driver, because motherboard on A1342 not have it. you may light up A1342 but without keyboard light regulation
Yes! Keyboard from A1278 absolutely capability (geometric & electric) to A1342 A1278 have another mounting holes, but it's may be fix I replace (in my Macbook White A1342) keyboard from model A1278, and all works fine!