I have an old 1890s-built Victorian home and I've been working on select repairs and restoration work over the past couple years. I have a front door lock that I would like to replace for functionality but one major difference I've noticed in this mortise front-door knob/lock set and others that I've looked into purchasing is that this one has the lock on the bottom instead of the top, which throws me for a loop every time I think about replacing it! Is this something easily interchangable or something I need to pay attention to when searching for a new doorknob? Also is keeping a mortise style my best solution. Thanks. Attached is a picture of the hardware we're working with.