Start with reading the tech tip on this site regarding truck wheels.
https://www.stovebolt.com/techtips/wheels/There are several types of split rims. If they are in good condition (not rusted or deformed) and If they are mounted by a knowledgeable technician, they are fine. There is one exception and that is the Firestone RH-5. It is dangerous regardless of condition. You may not have this type if the split rims on your truck are original to the truck, due to the age of the truck. Bias ply tires to replace what you have are available (not especially cheap). The other option, that is pricey, is to have custom wheels made to match your bolt pattern, but on a wheel that mounts modern radial tires.
You may have to find a tire shop that has experience with these type of tires and wheels, like a truck shop or one that services agricultural equipment. With split rims of any type you must use a cage or chains as you air up the assembly, in case things come apart. If you talk to old timers, they can tell you of accidents resulting in serious maiming and death.
Kent
