Joe: I've had good luck so far with a Kohler Magnum 18 which is basically a bolt-in replacment for a KT17; I've not had such good luck with a Briggs & Stratton 16 HP twin flathead such as came on the 582. The drive shaft connections are different, though. In either case, the ignition needs to be converted for use with magneto vs. a coil. I find it easier to use an interposing relay to convert the absence of positive ignition voltage to a ground contact to "kill" the magneto.
One fellow on this forum replaced the KT17 with a B&S Vanguard, but he had to rework the drive mechanism.