You currently have everything you need.
I have a set of secondary 40's I mounted as far back as possible and still allow the winch handle to work. I have an Asymmetrical, not a symmetrical spinnaker. As long as your kite isn't that fat, you will have a good working angle right to the winch. If you kite has a long foot you would need to mount a block as aft as possible to redirect the sheet back to the winch. In all honesty, for all of the additional work to mount the block 2 ft aft to redirect the sheet, you're really not gaining a whole lot of angle to the sheet line. If you have a high flying clew and the sheet angle into the winch is steep, you can set up something simple like a barber hauler or a snatch block to keep the angle of the sheet into the winch a lot shallower.