Hey Magnum WM,
I had a project about like yours but it involves taking the barrel off of a
GP-100 and replacing it with a Dan Wesson barrel.
Do you know what the threads are for a Ruger GP-100?
My smith may have to cut the threads on the Ruger and thread a sleeve for the D. Wesson barrel but I would have an interchangable Ruger GP-100
Happy shooting
Scott5