Here's a schematic for you to take a look at. It might be a bit confusing since there aren't any arrows or things that list directly where the o-rings go. But the o-ring size is listed close to the part.
http://www.icdproducts.com/paintball...hematicFS4.pdf
Just off the top of my head you'll need at least 2 017's in 90 duro urethane, a 006 also in 90 duro urethane. Those are the most important to get in urethane since the'll be getting the most wear and tear.
Then you'll need a couple 020's, an 019 and an 011. Those can be buna nitrile since they won't be used on dynamic parts.
