Went online and looked at the savage target action. Interesting that it has 3 trigger guard screws instead of the usual 2. I take it that the middle screw is still in the middle and that you need to move the two outer screws closer to the middle screw by .505. Hence the need for .005 accuracy. I think that there are several ways you could do this on your lathe. If there is no barrel on the action you could make a fixture that would hold the action crosswise on your tool post. Then you could move the action using the cross slide to the correct position to drill the holes. Or you could hold the action in a truing fixture with a drill chuck fixture on the compound and use the compound to move the drill chuck to the correct position to drill the holes. By using your lathe you can save the money for the x/y table to go to a small bench top mill.
Here is a thread on a truing fixture
https://www.hobby-machinist.com/thr...chuck-for-truing-receivers.90726/#post-831023
Here is a thread on a drill chuck fixture.
https://www.hobby-machinist.com/threads/shop-made-axa-toolpost-cross-drilling-fixture.49064/
By using the compound and cross slide you can get .001 accuracy.
You could also drill the new holes in the stocks. That would be easier than drilling the action. Put a transfer button (wrong term) in the two outer screw holes and tighten the action in place with the middle screw. Then drill your holes. Make the holes slightly oversize and epoxy bed the new holes. I would try this first before trying to drill action.
Just thinking off the top of my head on ways to do this.