Front Springs
There is usually no need to replace a front spring if it is not broken. With the front wheels on the ground, the front shock absorber arm should be about 1½-2 inches above the rubber bumper directly under the arm. If the shock absorber arm touches the rubber bumper with the wheels on the ground the springs are too high or “too strong”. As shown on a diagram on page 207 of the shop manual, there should be a distance of 4½-5¼ inches between the lower suspension arm and a point in the middle of the frame.
Rear Springs
The bottom of the ’49 rear fender skirt should be at the center of the rear hub cap medallion. More specifically, the ’49 shop manual has a diagram on page 208 showing the desired rear spring height. The center of the rear axle (or the center of the axle flange with the hub cap removed) should be 6-7 inches below the frame member directly above it. As these two surfaces are not in the same plane, it would be best to use two or more straight edges to approximate the linear distances between the surfaces. Note that the shop manual also states on page 48 that a variation of ½ inch is allowed in the rear spring height and that a variation of 3/8 inch is allowed between the right and left spring. The shop manual further states on page 48 that springs settle after installation, so it is best to wait 2,000 miles before taking these measurments to allow the springs to seat and settle. I had new rear springs installed some years ago and the back of my car was very high and looked odd for several months afterwards before the springs settled.