I agree there's no way you have "widow maker" Firestone RH-5° rims if you are seeing a three piece construction. Any of the three piece designs are safe to use if not damaged/badly rusted and are handled right. Your truck is at an age where the rims could be the older Kelsey Hayes "AR" design, or could be later Firestone/Accuride "CR-3" or "FL-3" designs depending on rim width, or could be the type simply called 5°. The important thing if you decide to keep your current rims is to be sure and keep the ring/rim sets matched. Mix matching is dangerous business. Here's an OSHA site that covers that. Stu

http://www.tireindustry.org/pdf/osha_Rim%20Matching.pdf