I am not all that familiar with the inner workings of the 645 but hope they are similar enough to the 1911 to give some advice...
How do the 645s come apart? How different are they than the 1911 design or are they just a slight modification? Do they have the same trigger set-up and if so do you think the pistol would benefit from a after-market trigger like the Chip McCormicks or Wilsons or someone else's???
If the set-up is the same, or similar to the 1911 you can also 're-tension' the center prong on the mainspring to increase the trigger tension and reduce the travel?
But, on the other hand, possibly one of our more knowledgeable members could kick in with more pertinent advice. Mikey.