My advise would be to stick -30mm Eibach springs on the front and use standard T30/32 springs on the rear.
I had Koni Actives with the lightest H&R -40mm springs fitted, which, whilst it was empty, sat and drove fine, but now I am using the van differently resulting in carrying more weight, it sits markedly lower at the rear.
I bought an Eibach -30mm, fronts only spring kit which I fitted together with my original T30 standard rear springs, and not only do the arch gaps look the same, but also the ride has improved further due to the increased suspension travel.
Its very common on heavy conversions to just drop the front to balance things out, hence why Eibach supply a fronts only kit.