When I used Scythe Kaze fan's on my MCR320, I used 2 inch 6-32 with 3 nylon spacers + a fan grill and the screws were barely not touching the internals of the rad. If you bring one of the screws you have to Home Depot and they should have something that lets you check the type of threading. If you can get 1-3/4 screws, they would be perfect, but if not a 2 inch screw and some spacers will do the trick as long as you have a few extra mm in front of the fans to spare.
Project: Black and White i7 920 D0 | 3 x 2GB DDR3 | EVGA X58 SLI LE
XFX 4890 | Corsair HX750 | Corsair Obsidian