Blue Jays- That exact topic was discussed in the Smithy forum awhile ago. Do a search for "length of pull" in that forum.
It mostly had to do with doing the job yourself, so I don't see why a competent gunsmith couldn't do it.
EDIT- Nevermind. I got bored and did the search myself. Wrong thread. Try posting the question in the Smithy forum.
[This message has been edited by boing (edited July 16, 1999).]