My ball screw kit came with 6.5x10mm motor coupling and I need 8x10mm. So I could drill out the ones I have. But I question how good these are to begin with.

They are an aluminum alloy slit type with small 2.5mm screws to apply the clamping force. Wouldn't a slit type with set screws be better than the clamping type, less likely to slip?

My steppers have a notch in the shaft for a set screw but the ball screws do not. If so do I grind a small notch in the ball screw shaft?