Converting interior mortise lock from skelaton key to thumb turn

We have several very simple 120+ year old interior mortise locks that we would lock to convert from skelaton key to thumb turn (since they are on bathroom doors!).
I have taken the locks apart and they have very simple internal mechanisms. It seems that I would need to replace the lever that is activated by the skelaton key with one that has a standard square hole in the middle so that I could insert a thumb turn.
I have previously tried adding washers to a skelaton key and putting those behind the faceplate to keep the skelaton key in place, but it doesn't give a good solution.
Anybody know how or whom I might use to do this conversion? (note it is an old locks so I assume it will need some combination of welding or custom fabrication)
The lock itself has a 2 1/2" backset with 2 1/4" between the spindle and the keyhole.
Thanks
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There are conversion kits available for this purpose.
However, another alternate would be to remove all the skeleton ket stuff, then use a high quality wood filler, like DAP's plastic wood, applied in small amounts at a time over several days. Once it's been filled in, just use a regular lock install kit and paint door. At least this way it will look like it's always been that way.
However, I am keeping my sleleton key locks on all my doors. It's simply easier just to take them apart, clean and lube then, and get the proper key for it, then reassemble.
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snipped-for-privacy@gmail.com writes:

I have searched far-and-wide on the Internet and have not seen such kits. Do they work on antique locks? Can you give me a link or reference?

I would prefer to keep the original antique character of the house...
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