I believe Ruger is doing a run of standard Redhawks with 4 inch barrel in .45 Colt-Delightful! A GP100 in .45 would be very sweet-even if a five shooter.
i'm not a ruger expert but that is either a typo or a conversion. the standard redhawk and the new 4" redhawks are i believe the only DA .45lcs ruger has made. but i could be wrong.
.45 colt just won't fit in the GP-100 cylinder. I've heard of a few smiths who will convert a GP-100 to .44 special, but .45 will not allow any kind of steel between the cylinder mouths.
The new 4" barreled Redhawk is chambered for .45 Colt as well as the .44 magnum. Maybe thats the revolver you are talking about. Been fixing to get one of those myself down the line.