Composite stocks may or may not be "drop-in" as claimed - depends on manufacturing tolerances. But they will be close, maybe needing a bit of sanding or removal of material with a Dremel type tool. Particularly check that the bolt handle is not touching in its recess, barrel is centered in the barrel channel, action sits flat and flush to were it should be.
Bedding is always a good idea to ensure a perfect fit. A competent gunsmith can do a bedding job or you can do that job yourself, just buy a bedding kit from Brownells www.brownells.com
(just make sure you use lots of release agent).
Your action is considered a long M-70 action I believe, even tho it is chambered for the .243. The McMillan M-70 Hunting is a great stock, and is usually available on the internet special.