For a stock mopar windage tray you don't need them. Mopar makes main bolts that have a taller threaded section to take the windage tray bolts. This set up isn't adjustable, but its better than no windage tray and works just fine, especially for more mild, non-race type builds.
If you go with a aftermarket windage tray (like a milodon or similar), they sell a main stud kit that also uses studs to intall the windage tray. This set up is adjustable, ie, you can position the height of the windage tray to improve its location and efficiency. You'd want to go entirely to main studs for this set up, and if you do that you should get a line hone to make sure the clamping forces with the studs are equal.
