I just went throgh the switch on my 1984 500 SEL. As far as I know the suspension system are the same between Your car and mine although the actual components are different so You should be able to do the swich. You probably need to change the rubber pads on top of the spring to get the ride level correct.
To most difficult thing in the switch was to get the rear springs in. This was a real PITA and I broke 3 spring compressors and an air torgue gun in the process.
I´m happy with the conversion and the car actually rides better now although a bit on the harsh side.
My reason for not keeping the hydraulic system was that the pump leaked hydraulic fluid into the engine so I did the math just like You and did the switch.
Be carefull though with the springs and get some good quality compressors because with the layout of the system the springs are as strong as some light truck versions an should ba handled with some respect (except verbally in my case).