how do you mean its hitting the rear of the wheel? the spokes? cossies came with a different offset so wheel spacers may be needed, have you tried it with the disc on? have you got the right amount of spacing on the caliper bolts? are u sure the caliper isnt fouling on the wheel balance weights?

dont you have the calipers the wrong way round? from what i heard the bleed nipples are usually round the bottom when you do the cossie conversion as ive heard people saying its a pain in the arse to bleed