If you convert to a deffy front axle then you either have to mod the axle for leaf springs, or mod the vehicle for coil suspension, the former being the better as modding the suspension on a series might bring you in line with the SVA test, which you dont want to do.
I looked at modding a disco front axle for my series, but thats a world of poo as well, it can be done, but loads of hassle.