For the fronts, nothing will fit if you don't cut the stock holders. Outside of that, i think you have a pretty good depth. My kappa componets fit with no problems at all. My kappa 3 ways just barely fit on bottom and on top.
Anyway, i think you should be fine on the front. For the back, if you need to use a spacer, you could always fiberglass a bit more material on the stock grills. Usually you would just replace the grill but it has the guide for the seatbelt. Then just be creative how you attach it. I'd probably epoxy some wood to the bottom of the grill, then drill into them from the bottom.
Or you can cut out the grill section carefully and then put and aftermarekt grill on top of that, giving you more clearance on top.