Measure old fork distance axle to crown and compare to new fork,im guessing it wont change much compared to reg fork.Suspension corrected rigids from what ive seen are based on 100mm travel....only changes distance by 13-20mm anyway.So an uncorrected fork will drop nose of bike a bit....its usually not a big deal.Im thinking an 1 1/8" threadless is way to go along with an uncorrected rigid fork.Lot better stem selection for threadless these days