I doubt the problem is with the spring(s). I would suggest taking the spring off of the shock and feeling its dampening action prior to install. Anything but smooth operation is trouble. I have two sets (one NOS that I paid good $ for) of those alloy bodied Konis acting as paperweights in my basement. Why? The internal plastic parts tend to turn to goo and muck up the oil passages. The end result is erratic compression or even total lock up. Disassembly, requires fabricating a custom spanner and once you are inside there are difficulties with cleaning, particularly the piston ("dissimilar metal" locked to the shaft) and the foot valve (which has a bazillion pieces all set under proper tension by the factory). I purchased some of the rebuild parts from Ikon but was never able to get things properly cleaned and reassembled. . . .Hope you have better luck than I did.
PS, if you find that your shocks are OK, measure their length and I can compare to my sets for the 750. I have a few sets of springs that might work for you.