I was going to post this picture last night, because it sounds like you might not have seen an actual Flint to Percussion conversion, but couldn't get to it.
So, this is a very typical conversion, on one of the guns I have.
On the front end of the lock, the two red arrows are where the Frizzen spring was mounted, and the mounting holes are now plugged.
Above that, the small black arrow is the threaded hole were the frizzen was mounted, now plugged also. The Pan would have been where the percussion drum is now.
The bolt end at the far right hand side is the end of the forward lock plate mounting bolt.
The dark circle between the two red arrows is the end of the Main Spring mounting pin.
And just as a point of history, the practical use of percussion locks in the US didn't come about until late 1820's / 1830 in rural areas, and even later in the back woods.
Good luck with your search!
John
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