We are in the process of building an addition to out 1940s house. All the existing doors have mortise style locks, antiques knobs and back plates that are original to the house. All of the keys are missing. I would like to replace the locking mechanism but keep the antique back plates and knobs. For the new doors in the addition I want to use several antique knobs I already have. How can I use old knobs and back plates with new locks? Thanks for your help!