Ok .... the original ZX5 used a king pin ball stud and king pin that were sized to suit the hole .... they ran without a top hat so the bearing surface was between the ping pin and the plastic hub. Your original ZX5 kit parts will work perfectly well on the SP plastics ... trust me!!!! (I'm an automotive design engineer if that helps convince you I'm not completely mad regarding such things!)
You will need to space out between the hub (254) and knuckle (222) with a plastic washer. The gap is slightly less than 1mm and the king pin is 4mm OD so what I did was take a 1mm plastic washer, drill it out to 4mm and then rub it down on some fine wet-n-dry until it was a sliding fit.
ALL of my set-ups for the SP on line were running this mod .... it ran perfectly for well over a year of regionals, nationals and winter series!
Have a look at your original ZX5 manual and you will see how it went together .... only thing you need to do differnetly is make up the spacer washer
