O.K. You will have to re-drill at least one hole, the front screw in the trigger guard piece. Also, depending on the age of your Blackhawk, the vertical lugs of the trigger guard may be a little short. This where it mates to the back of the cylinder frame. Later model Blackhawks are slightly deeper here to account for the Bisley grip frame. You will have to make a seat (a pin) for the trigger spring. And, as you mentioned earlier, a seat for the mainspring.
If you were to have these in hand I'm sure you would readily see the work required. Some fitting, too much for some, maybe only a small task for you.
By all means, if this does come to fruition, please, please, post a photo.