Aside from whether the headtube is long enough, there are two major measurements that will mess with the handling of the bike: Rake, and Axle-Crown length. Rake is the distance that the center of the axle is from the center of the head tube axis (some folks call it offset). Axle-crown length is the "height" of the fork, the distance from the axle to the base of the crown, where the crown race of the headset sits.
If either of these measurements is far off from that of the original fork, it will mess with the handling.