Don't know what brake setup you have - mine is sierra front discs and sierra drums at the rear fed by an MX5 master cylinder and servo. To get the balance right I removed the rear sierra brake cylinders and replaced with Ford Ka ones.Physically exactly the same dimensions. Can't remember exact internal dimensions but the pistons inside are 2.2 cm? sierra and 1.7cm Ka which has the effect of reducing braking effort to the rears. I also kept the MX5 pressure regulator but one is also present on the sierra setup which simply inserts in the pipe line to the rear brakes. Both these measures kept my car well within the limits required by IVA for front rear balance.
Hope this helps