1.75u space is only used on a few staggered 40% boards and nowhere else. To be exact, the keyboards it's used on are: Vortex Core, JD40/JD45 (the latter requires 2× 1.75u).
If this set isn't going to have staggered 40% support, the 1.75u spacekey can be removed from the Split Spacebars kit. Actually, it should be removed from this kit either way.
I would recommend adding a 1u spacekey instead, which is useful for Alice (2.25u+1u left space configuration) and similar ergo boards.
A second 3u space might also be worth your consideration. There are indications that 3u+1u+3u will be a popular split space setup in the near future.