Red 49 Truck,
Lightholder's Dad is correct. Pics would be a big plus to get started on the proper door latches and strikers. For what it's worth, I too have a late '49 3100 that I had the same problem with. I purchased aftermarket latches and strikers and had little to NO success. The latches were poor quality and I ended up returning them. I purchased two sets of strikers from two different vendors and after careful measuring of the riser for the safety catch I found that the aftermarket strikers were 1/8" higher than the original worn strikers I removed. Long story....short, I ended up buying a set of NOS door latches and NOS strikers. Lined everything up, adjusted the door gap on both doors with the hinge adjustments to specification from the 1948-1953 Chevrolet shop manual and the door close perfectly! Original GM parts do make a difference along with a lot of patience. Finding these NOS parts are difficult, but E-Bay, swap meets, and some parts dealers on the internet who have purchased old Chevrolet dealership parts inventory would be you best bet for these door latches and strikers. You could also post an ad in the "parts wanted" section of the Stovebolt forum and someone might have them.
Tim