I've hacked mine all to hell trying to get them to fit as-is. Don't waste your time. I had a guy who has built a dozen or twenty of these same model cars and he said they always cut theirs. Now the reason he gave me at the time didn't make any sense to me so I wasn't going to cut mine. Truth is, regardless that he didn't remember why they did it, the point was to cut them so they're easier to install. And makes everything fit well. I should have cut mine. I will be cutting mine now and I think I can do this with them installed into the body and the body fitted to the frame. These pics look better than the final product because you don't see it installed onto the body. It's currently a mess. I'll shoot pics before I tear into it. So you can see how bad things got. I guess I'm glad I screwed up my mix and made it without enough hardener Because I would have been cutting them out had they setup properly.
The pictures I have here are all of the progress on the way up to where I am now. I made the screens in front of the radiators an integral part of mounting the radiators to the boxes. You'll see where I welded washers (doubled them up) to the screens to make them mounting points for the radiators. And then of course the screens are also screwed to the boxes.
Another tip, don't ever mix large batches of fiberglass at once (unless this is your day job and you know how to get the hardener just right), keep the smaller more manageable batches going and just pick up where you left off as you go along.
Here are the pics.