Hi, I'm updating from my Movable Type 2.5 installation, and I'm considering using MT 4. A big concern that I have is with the permanence of my URLs. With my current installation, a post titled "The Reasons to Upgrade Moveable Type" would read: thereasonstoupgrademoveabl.php, however, that post on my old system would be thereasonsto.php
I've looked at the archive File Path Specifiers: http://www.movabletype.org/documentation/appendices/archive-file-path-specifiers.html
but don't see anything about changing the number of characters that filenames are truncated. Is there a way to do that? Or is there another way that I can upgrade without messing up my URL structure?
Thanks for your help.

This is accomplished under the Preferences menu of Movable Type. Under the Entry Settings area, change the "Basename Length" to 50 or so. That is what controls the max size of your entry basenames.