Those really do look like the RH5 "Widowmakers". Give this legacy
Wheels Tech Tip a read and look at the attached pictures. It should help you fully ID them before you attempt to work on them. Also some insightful info on replacement wheel and tire info, but the tip does date back to 2008.
If you want to read more current info on the Big Bolt wheel and tire topic, use the
Stovebolt Search link to find posts related to what you want to know more about.

On a slightly different note, while your looking through our
"Legacy Tech Tips", you will find at least one on your previously mentioned topic on basic info about your
"Dump Body".