I assume you have already test fitted the dash top, before preparing to cover it. I understand they can need some fettling, due to manufacturing variations (probably a much by Lotus as Banks)
You're right. Most of them need trimming (a dremel with a cutoff wheel is your friend.) a bit to match the outline of the lower windshield opening curvature. Couple hints/suggestions from experience:
1. Test fit and trim the bare fiberglass eyebrow BEFORE covering it.
2. Check to make sure the flange where the instrument panel sits is a 90 degree angle to the bottom or the eyebrow will tilt down when you tighten up the instrument panel mounting screws. Gentle application of heat gun on low on the back where it is folded will soften up the resin a bit and let you work the lip to where it should be.
3. When you finally get to attaching the vinyl...leave the edges long on the windshield edge. Trim it back to leave it about 1/2" (12mm) long, and use a length of door edge trim (black) to capture the edge and fold it over to the inside on the edge. It helps finish off the edge, and stabilize the vinyl so it's less likely to pull back. Doesn't hurt to put some contact on the inside of the eyebrow along that line and the vinyl to help it stay where it needs to be. Take a look at the photo below (it's my old S2, #693R)
4. Take your time trimming the fiberglass. Better to test fit a few times and work towards the final adjustment than to attempt to do it in one fell swoop.
5. It's easier to do with the windshield out. But...if you've not the experience of removing the windshield...there is a 50-50 chance that it will crack while attempting to remove it. Not the end of the world if it does (since replacements are available), but, like many things in the car, one job often requires attention to surrounding items to get to where you want to be.
