Using the chart on Texas Grips' website for Ruger revolvers, I don't think these fit the Ruger Dragoon grip frame. Texas Grips calls it Super Blackhawk but notes it's also referred to as Dragoon.
Using that chart, perhaps it's the XR3 gripframe it fits? Looks to be the closest to matching the dimensions you provided.
Just food for thought--lovely grips one way or another.