I ordered a replacement screen from ifixit, but contrary to the description it arrived without the ancillary parts attached. So I had to transfer the front camera & sensor assembly, and the lcd shield. In case anyone else needs to do this, be sure when transferring the lcd shield that the screen cable sits properly underneath it (ie as far up towards the top of the screen as possible) or else the rectangular block on the cable will foul the loudspeaker.

If this happens, the bottom right corner of the screen will stand very slightly proud of the case, and you will end up with a pressure spot on the screen.

See Pressure spot on iPhone after screen replacement..