I've done this to mine with refurbished mk3 mondeo calipers and mk1 focus ST discs
When I was weighing up the options of ST170/mondeo calipers, I heard it was easier to get pads for the mondeo calipers, but don't know if that's actually true.

This guy sells a full kit with refurbed calipers for £200, which isn't bad considering by the time you've got all the bits it will cost about the same
http://www.sico-developments.co.uk/c...iant=381203548

As said above, you need to drill the hubs from 10mm bolts to take 12mm bolts (which isn't hard)
If you don't get the bolts with the calipers, ford charge £5 each for them, so I got some grade 10.9 zinc-plated ones for 50p each
No need for spacers if your wheels are the standard ST 17s (but note the spare wheel won't fit after)

Cost me £70 to do it all originally, but the first set of cheap old calipers I got siezed and warped the disc so I had to buy the whole lot again. Second time around I went for EBC 'GD' discs and greenstuff pads, here it is: