COLEYST200 is correct, there were 2 different sizes of discs/callipers on 2.5l Mondeo Mk1/2. One size was the same as the I4 engined ones. I had the same problem in identifying what I had on my ST24. Easiest, if the supplier can't work it out from the VIN, is to measure the actual disc diameter.

Its certainly worth looking ahead and having a set of MK3 callipers (and 4 x 3mm spacers) ready for next disc change so you can just fit 300mm ST170 discs.