Using a bit instead of a crossover saves 6 ramps off the book solution:
https://lodev.org/jstumble/?board=rlerrf1lfrrfe1lfrrfellfrrfellfr0eei_8_8
Or, if you allow bits and crossovers, the total part count can be cut down to 19, still with no extra red balls in the output (inspired by @NickP’s solution):
https://lodev.org/jstumble/?board=rlerrf1lfrrfe1lfrlfexferlfexfer0eei_8_8