That can work. I have found that round "barrel" type slides are more prone to jamming than flat slides, though, especially if they are undersized. That said, Allslip slides tend to work pretty well. Also, Selden offers some slides with rollers on the outside that are made for full batten luff boxes and internal tracks, but you might have trouble matching them to the slot in your mast extrusion. If you have an external stainless track that takes "C" type slides, you might want to retrofit the Tides Strong Track or the Bainbridge external track.
One other thing to watch for is the fill to warp ratio of the cloths being specified. For example, Doyle is correctly specifying a high aspect cloth. Quantum is not.
The warp strands are those that run the full length of a bolt or panel. The fill are the strands that go side to side (as does a shuttlecock).
On a crosscut sail, most of the stress is across the panels in the fill direction -- that is, up and down. So the fill should be heavier than the warp by approximately the aspect ratio of the sail. Your aspect ratio is about 2.8, making it a high aspect sail (high aspect typically considered to be anything over a 2.5 ratio). So ideally your fill would be in the ballpark of 2.5 or more times the denier of your warp. Contender 6.4 has a ratio of 410/250 (1.64), more suitable for a low aspect sail. So depending on conditions in which you choose to sail, it might be slightly heavier than it needs to be, hurting light air performance, or somewhat weak in the vertical. If you like going out in the heavier stuff, maybe have the panel seams reinforced at the leech, or you might want go to the 7.4 if Quantum can't offer a good high aspect cloth in the 6.4 ounce weight range.