I think I have grid-staring stupidity setting in. Firstly "one part split" is a little misleading as I assumed it was one of the 4 parts, not one of the thematic items. Secondly, I haven't a scooby what the message from the down clues (5,5) means and finally 47+26=63 leaving 93 cells. An earlier post suggests those of the 47 in peripheral columns form part of the 103 - but why? Only a hint please - nothing else.