Cheers guys, that explains it. I wonder though, why these aftermarket (Thailand sourced) cables use the smaller ferrule size? Wouldn't it be smarter to make them to the larger size, so they fit all vehicles which they claim to (ie. you can drill/file out a small hole, but it's not so easy to shrink a larger hole!)?
The only easy option for me now seems to be to carefully butt-weld a thick washer or similar with a 14mm ID over the ferrule outer to increase its diameter. And source new clips as the ones intended for the larger ferrules are slightly too big for the smaller ones (I have 2 off an S15 200SX at home that seem to fit the smaller cable ferrules perfectly, though I have no idea where to buy another 2 from!)
I could mod the car, but working on the brackets attached to the chassis will be a pain. I'd have to weld-fill and re-drill the holes.