I doubt it would be all that much of a difference. Even if it dropped down to a 500lb spring that’s still 1000lbs for 1” of travel. As far as I understand it the IFS has the spring mounted say half way out on the control arm and uses a lot of leverage to compress it. I hope I’m not totally screwed up on spring rates here. On your setup it’s like a 1:1 ratio compressing the spring where it’s gotta be 3:1 or something like that? Hence the heavier spring rate. With a 560lb spring it might end up with the shock being most of the way topped out. Just my .02... like I said I’m no expert on this stuff. I was just thinking about doing the same thing with my wife’s 11 Ram 1500. I had a set of axles out of a 3/4 ton and tossed around the idea of using the struts that are on the ifs as they aren’t factory.