I've got the model in 3dsMax right now and I can tell you exactly what's causing the problems.
The zigzag you're looking at is caused by unwelded vertices down the middle of the hood.
And the rest of the exterior problems (all those unnaturally dark areas you see around edges) are caused by extremely bad smoothing groups, whoever set the groups never realized that you're not supposed to smooth around 90 degree corners....
Plus there's flipped polys all over in random places, whoever made the model did some parts really low poly and other parts really high poly, and some places are really messy.
The exterior body is literally cut in half, and the top half has parts of the lower half and vice versa.
And the shadow is from the Countach, and the low-poly distance model is from the Murc Spyder.
When you look at the unsmoothed model, it's actually pretty decent quality and if all the bugs were fixed it would look really good ingame, but right now, the smoothing groups kinda ruin it.
If Grin wants, I can rework the smoothing groups completely and send him the results, but it would take a few days to get it all done right. I might even be able to do a proper shadow model and distance model, duplicating parts is easy in Max.