Krist has changed, they are now 6 shots and you can purchase with or without the loading gate. Howell did at one time held the patent for the design of their 6 shot cylinder. Thanks for posting.
Not seeing a loading gate for the ROA on Kirst's website - sure you can cut your own. Maybe they figure very few people are going to cut up a ROA.
http://www.kirstkonverter.com/shopdisplayproducts.asp?id=4&cat=Ruger+Old+Army+Konverters