I'm not familiar with the Harley hub you have, but as long as they're the same number of spokes: measure the the distance from one spoke hole to one directly across on each hub. Add or subtract 1/2 of that measure from your spokes, depending on whether the Harley hub is a larger or smaller diameter hole to hole. If you're using some tricked out lace pattern, then all bets are off and you'll have to take a class in Geometry and Trig to get your calculations. I used my method more than once, a long long time ago when I was lacing Triumph sprung hubs to Harley 16" rims for rigids.