Tseaha,
You might give Ten Ring Precision a try for that .45 cylinder (
http://tenring.com/firearms-single-actions/ ). Back in the "good old days" they were one of the premier retailers for USFA and I believe that they still do some work on them. Their web site indicates that they still have conversion cylinders for sale but they are pricey. $395 for the cylinder and $45 for custom fitting to your frame. Sounds like you have a pretty nice hybrid SAA going there. It might be worth the money.
I recently gave a 4&3/4" USFA .45, with .45 acp conversion cylinder, to a very old (we've been friends for over 60 years), very dear friend of mine who resides in St. Johns, AZ. He was using a .22 with shot shells to dispatch rattlesnakes on his property. Needless to say, he is now much happier with the .45 shot shells. Carries it in a Tom Threepersons rig that he got from El Paso Saddlery and will never go back to that .22. He uses the .45 acp cylinder for target practice and has found it to be quite accurate.
By the way, welcome to the USFA forum. Hope to see more of you here. Should you contact Ten Ring, let us know the outcome.
Sincerely,
CJF