Mine came with the conversion kit as part of a trade. It's dead simple to change the cylinder on a Remington compared to a Colt "wedgie". I know a guy who had several Colt-type cap & ball revolvers and he had cartridge cylinders for all of them as he didn't like BP and the associated clean up. He didn't last in the CAS game. Go figure .....
I think the figures you mention refer to the length of the cylinder. Ask the maker for confirmation. If you order, give them the details on your revolver they will send you the appropriate model.