Here are some photos of my Ruger Old Army with a Howell conversion cylinder. I included one of the quick change Belt Mountain cylinder pin units.
This set up also is giving me very good accuracy. POA is no problem with this ROA since it has adjustable sights.
I read someplace that a guy questioned the ammo to use in a Kirst conversion. He was allegedly advised by Kirst to not worry about it since it was an ROA. I am using standard pressure Silvertip HP ammo and the fired cases almost fall out of my RD cylinder. if I find another ROA I may try a Kirst system in that one.
Also, I like the idea of using a Kirst system in an open top 44, I will have to try that.
As a side note, I just checked with the head of the Michigan State Police firearms registration unit. It looks like simple drop in cylinders with no firearm modifications do not have to be registered in Michigan. If you have to modify ("re-design" according to ATF) the gun, then you have to register it as a modern firearm. This definition may vary from jurisdiction to jurisdiction.
This is a great thread and thanks to 45 Dragoon for his comments.
Trooper Joe