Here are the step by step instructions for building the spectrometer that I am using at this moment
This is the view with the forward face cover on. ( it would be covered when doing fluorescence spectra, then you would remove the plug on the side for your 90 degree angle.) do the opposite for absorption spectra, remove the front cover and place the plug back in the side.
The cuvette holder is designed to accommodate both forward facing geometry and perpendicular geometry as well ( 90 degree angle.)