Number of holes must be the same, axles, spacers and such can be adjusted and made to fit your application. You also have to make sure the angle of the holes in the nipple will work with the diameter of the hub you want to use. I like lacing large brake drums into my rims and you have to make sure the hole in the nipple is as close to the edge of the nipple as possible. If the angle isn't right there will be a curve in the spoke when mounted. This can be quite prominent depending on how far off the angles are. Believe me it's not hard, if I can do it anyone can, but it is kind of nice knowing you had control on another aspect of your build.