You need to match the steerer tube diameter and, if threaded, a near approximation to the original length or, if threadless, you will have to cut the steerer to the correct length. Also, you want to closely match the crown to axle length, that is the distance from the base of the steerer tube where the crown race sits to the center of the front dropouts. I'm pretty sure this is a suspension fork, so the a-c distance will have to be approximated by the compressed length with your weight on the bike or the fully extended length if the forks have the same amount of travel.