The name of the man who took over the manufacture of the RPM when Jim finally retired (about 2004) is Gary Wrigley. I believe that Gary lived in or around St. Louis. He's Jim's son in law.
There was a long time serious rift between the IHMSA and RPM going back to the price ceiling days, thus I doubt you'll get any leads from them, even though Gary was once VP of IHMSA, following the origins of the rift under Elgin Gates.
All of the RPM .225 wildcats involved a simple neck-up, without "improving" the case. Jim once told me he wanted "simple, easy to form" wildcats. I own a 15" RPM XL in .30 Merrill, and like the cartridge a great deal. I think I once asked JD if he was interested in such a cartridge, but as I recall, he wasn't. JD's machinist Dennis Lawrence handed me a .30-30 AI at that time, and commented that "this will give the same performance". I agreed, but commented that the .225 brass is a bit stronger, to which he agreed.
As to your comments about personalities, I have called both JD and Jim my friends over the years. I have known both of them (and many, many others) to come across as gruff from time to time, as well as to be extremely friendly and courteous at other times. I'm sure some people would say the same about me.
My own view is that asking a person to supply drawings or information , without compensation, for products that help supply a living and livelihood for him and his family will vey likely not meet with success ... and I for one, certainly understand that.
