I'm in the process of installing cylinders and pistons from a 1997 700 SPX to my existing case reed motor which is a 1996 XCRsp 600. I noticed in my manual that the needle jet is supposed to be a #247-Q2 and my existing carbs are a #247-P6. Can anyone tell me the difference and if I should definetly do this change. I'm just not sure what the difference is.

yes, big difference. swap the needle and needle jets. they should interchange.