Quite right not to file them(4mm), as you have found out they won't for a cossie or rst disc as these are 24mm wide.
So ideally you need a disc from a ford that is vented and 20mm wide, going to seriously struggle with this.
Some can be seriously tight when new getting things squeezed in, I have often had to just skim a tiny amount of the pad away, where it was a bit "hairy" being new.
Your best bet is to see what the calipers are like on the car ie would the disc fall in the centre without the pads, if it does, then you can just get a local engineering firm to make some wider spacers for the caliper halves, but if also needing to space these outward due to diameter would be better off selling.
tabetha