Thanks for your effort and I have taken a look into your designs. About the lever, I added the fusion file of my version to this message so all the features can be adjusted. I will keep my own file because I have the adjustable source files of this one and if more people are facing similar issues I will create a new version. For now I am happy that yours works great!
About you z-axis stop: it looks good. I have a couple of remarks/suggestions. First, I would not place all these little fillets because the printer does little to nothing with them, there is always a fillet of the radius of the nozzle already and the gcode becomes smaller. Second, I think the side on which the spool is screwed on is too thin. I don't think if you place a 1kg spool on it that is will remain horizontal. Third, there are two very thin sides where this large nut goes for the spool holder goes (almost 0,4mm thin). You could make this thicker or rotate this hexagon 30 degrees. And last, I would line out the holder with the back side of the frame this will make it sturdier and it will look better I think. I always try to keep my functional designs as simple as possible, this increases toughness and is better for printing.
I think the idea of combining a spool holder with z-braces is great, thanks for sharing!