Griffith,
After you get your Open Top set up, consider this. You have THE most VERSATILE single action on the planet. First peruse Pettifoggers tutorial over on "The Open Range" paying particular attention to correcting the Barrel to Arbor fit. Then if you desire, at a later date, and after saving up your box tops, you can purchase Barrels and Cylinders for all the calibers the Open Top is offered. .45 (I don't recommend the 45) and .44. Once the Barrel to Arbor fit has been corrected, additions will install with only minor fitting.
Coffinmaker