Your wheel stud thread size is 7/16" x 20 according to this screenshot from a Chevy Master Parts Book (below). Sounds like the wheels you purchased look like this one I found in this
evilbay ad. Many good pictures. especially of the reverse side showing the casting identification markings including your mentioned "RW1".
You might find it easier to take one of your wheels to a local wheel shop (if you have one) as they will have a wide variety of the barrel style mag wheel lugnuts and washers to make sure you get the correct length lug nut. Let us know how it turns out.
