Yeah, what you are wanting to do is entirely possible. Before you start, however, I want to warn you that parts for many laptops, especially older ones, can be a pain to find. Inventory what you have and determine what you need before you just start buying stuff. I am sitting on an i7-720QM because I didn't plan ahead, as well as a few other parts I have no use for.
As for 'if it fits,' I am going to caution you again. Laptops are not desktops. Their design is nowhere near as open or as universal and older machines are worse. You could have three laptops with rPGA 988A sockets and have each one only support one or two processors, all with no overlap. If you need or want parts that weren't part of your machine originally, it is a good idea to check if the parts you want were ever even offered in it or its related models. For example, I have a Dell Latitude that the Gen 1 i5 and i7 mobile processors both work in, but not the i3 chips. It solely a BIOS issue. It all fits together, just won't work together.