Is it possible to convert??

You are changing the dynamics of the entire situation. This is sort of like two guys holding a weight, let's say you have a device sort of like a stretcher with a guy at each end, and a weight "down towards" one end. One guy has more of the weight. If you TILT that weight the guy on the other end has to hold up even more of the load.

Ok, as the rear of the car gets higher, I thought the shackle side of the spring would see less weight not more. As well as the weight of the rear of the car would be less and the front wheels would see more of the weight.

I guess I'm just not seeing it. I'd like to see someone use a scale to measure the weight the shackle side of the spring sees with different shackle length. Could remove the shackle and use different lengths of wood blocks to simulate different shackle lengths.