Talked to Kirst Konverter folks.
My contact at Kirst was Jay (firstname.lastname@example.org) on October 4, 2010.
After shipping my 1858 Pietta Remington to Kirst, Jay quoted as follows:
1. $80.00 to cut a loading channel in the frame (you may not want this - you can just remove the cylinder, remove spent cartridges, load more, put cylinder back in). But sure is easier to just load cartridges thru a loading channel in the frame, without having to remove the cylinder.
2. $20 for return postage.
3. $265.00 for the appropriate Kirst conversion cylinder for .45 LC.
4. They will make sure you can still use the original cylinder for cap and ball, as well as the conversion cylinder for .45 LC cartridges. So you can go back and forth.
5. They will adjust and fix any timing issues that come up (rareley needed), all for the same price.
Total $365.00. Sounds like a deal to me.