Help needed

Hi I'm in the process of doing a little work on my camper, its a little low atm so raising using the torsion bar at the front & now moved onto the rear uprating the shocks & springs, I've run into an issue in that I can get a shock no problem, was thinking of using the koni heavy track, but as for spring I've hit an issue, I want to raise the rear around one and a half inches, so need to know the dimensions of the original rear coil springs to ascertain whether they are a lowering spring that's fitted or original to let me know where to go from here, either replacing with standard or having a specialist spring made to suit my purposes.I basically need to know the dimensions of the rear coil spring on the slwb RZH-132 variant & I'm finding this info very difficult to come about the original part number is 48231-26100,can anyone help???