I have nearly completed the build but have 2 left over springs, and a 4 edged plastic panel a few cm in size. Any guidance for where these go would be much appreciated.
Not 100% sure about the springs, but the plastic panel is probably the truss rod cover, and fits on the headstock over the truss rod channel.
If the two springs aren't large, then they are probably meant to sit between the single coil pickup and its pocket as the height adjustment. The humbucker height adjustment springs come pre-fitted to the humbucker rings, but the single coil pickups will be loose, along with the two mounting screws.