lilja....Hart...Shilen.... pick one
midway, brownells, Boyds, B&C, etc....pick one
The action doesn't need anything "improved" unless you don't like a specific thing.
I have a stock 10FP from a decade or so ago(308) that I shoot 1K all the time. If you are lucky enough to have an old 3-screw trigger, do the adjustments, buy some good glass, and a stock that fits your shooting req's.
If you are chasing 1,000 I REALLY recomend something like a Choate U.S. for the weight. Helps with recoil, if you are a several hundred round per outing shooter like me.