I think I can answer your question, though I think Jim has already tried from another poster.
The lock he is inletting for is Chambers' Late Ketland flint lock. At this time, Chambers do not make a percussion model of it. So in order to make your rifle percussion ignition, you would have to convert it just as a smith would have in 1830...cut away the pan, leaving/or not, a remnant of the fence, take off the frizzen and spring, plug/or not, the holes for those parts, make a drum and install it in the barrel. The plate would have to have a semi-circular cut out for the drum as well. This is not a difficult job to do, but would require patience and a good idea of what the finished product should look like. Then, a hammer added to the lock with the correct throw to align with the nipple.
I've ordered Jim's parts set for a young lady who want to build her own rifle...I know this next statement is heresy...maybe I can talk her out of the flint and into a percussion rifle? I would be happy to document the above process if that is the case.