In all the gunsmithing manuals about Mauser rifles, it is clearly stated that Mauser type triggers should not be set below 3 to 4 pounds for safety reasons (spring tension, sear engagement etc..).
As for aftermarket triggers for the 1640 series, you still can look for a Tradewinds - HVA trigger, which was made by Timney and is designed to use the orignal safety lever, but they are hard to come by.
You can also use M/98 adjustable triggers such as the Timney Featherweight or Sako (very hard to come by, but certainly the best trigger a Mauser can use) even the Parker-Hale triggers, the only thing is that the original safety lever won't work anymore and you will have to make a notch inside the stock to have the new trigger safety work, and it will only lock the trigger, not the bolt.
You can also install or have installed a Hubber Concept Anti-Friction Ball Trigger, which should help a lot. You can also drill a hole in the back, below the sear and install the original pin so the original safety lever still works.