I am not quite sure what the actual problem is, but I guess the combination of wheel offset with the spacers on both sides of the brake discs. ET35 is normally the perfect offset for wheels on a Cosworth, but that is of course without spacers. Personally I would not like to put spacers behind my brake discs, in fact I am not a fan of spacers at all. The disc offset on a 2wd Cosworth is not that low, so I don't really understand why the disc needs the spacer behind it. What car do the discs come from? A common upgrade is mk1 Focus RS discs, those discs have a lower offset (52.7 mm) than the 2wd Cosworth discs (55 mm). I'm not sure if this is the distance to inner or outer disc surface. If it is the outer surface the Focus RS discs might be 1.7 mm closer to the tie rod end, as the Focus RS discs are 28 mm and the Cosworth 24 mm. But 1.7 mm should not be a reason to run 5 mm spacers.

Apart from that I'm not sure what wheels you run, but it sounds like the Ford soft spokes. The soft spokes are quite bad for caliper clearance, so in the end it might be best to change wheels, even though you have the correct offset at the moment.

But what does this actually has to do with going back to Koni shocks and standard ride height springs?