I may take Sir Charles' method and just do the 6.75"barrel.
Which ever length I decide on, I will cut the catch and sight out of the off-cuts and try and form the dovetails from the barrel parts they are still attached to. (Both pistols are stainless, trying to retain the original look).
Thanks to all of you for your advice, AE.
PS, thanks Flint, but I try to do most of my work by hand, and we don't have Brownells over here!