Very often the holsters will have enough leather to make the fit but will just need for it to be reshaped a bit. If the holster in question does not have a lot of fancy tooling that needs to be preserved then wet reshaping is usually easy to accomplish. Snip off an appropriate size and length of wood dowel, tape it in the correct area to create the necessary shape alteration. With that said, many holsters made for the cap and ball will not even need alteration for a conversion unit.