I fixed my old 4 slider in a similar way. I ground out the slots on the shifter stick ball until they matched the width of some (I think) M4 hex head high tensile screws. I drilled out where the roll pins went and put the hex head screws in, heads inside and nuts outside. I think, as I recall, I threaded the roll pin holes to take the M4 screws also. This repair worked really well.
