disco rear brake upgrade

Hi guys, have upgraded the front nrakes on my 300tdi auto with 110 calipers and vented disks, thing is now I have a set of the old 4 pot solid calipers and was wondering will they bolt on the back axle to replace the 2 pots. I know i would proberbly need a brake bias valve to get the front rear ballance right but just wondering will they physically fit.