I think it would be a custom job. There is a picture of one in Dennis Addler"s book on cartridge conversions that was done in the day but the trigger and guard are much larger than in the picture you show. I have thought that if ever bought one I would want to do the same thing.
How many of these were 'done in the day'?
Also, is the one in the picture (with the smaller trigger/guard) an original or a replica?