Yes, the iPhone SE looks and feels strikingly similar to the iPhone 8. But can you swap a few of their internals? Well, a teardown by iFixit suggests that you can do that for a few parts, but not key components such as the processor or battery.
iFixit says the iPhone SE’s cameras, SIM tray, Taptic Engine, and display assembly (including the microphone and proximity sensor) can be interchanged with their counterparts inside the iPhone 8.
What about the battery? You can’t. That’s because even though they look identical, the logic board connector of iPhone SE’s battery differs from that on the iPhone 8. Also, the Touch ID fingerprint sensor can not be interchanged, and you have to pay Apple for a replacement if you damage the one on your iPhone SE.
Moreover, if you fit the iPhone SE with the display from an iPhone 8, you’ll lose the True Tone property, which means colors won’t look as natural as they do on the iPhone SE’s original panel.