It's a very tight squeeze, you have to essentially remove all the plastic supports inside. It's also unlikely you can fit 18650s, so you'll have to use flat cells. They sell screens that are the same size as the original, so you can easily get that in there, though you'll have to relocate some of the taller components so you can fit the driver board.
However, if you make a spacer to make it a little thicker, it's much easier to fit everything in there.