Honestly, I have to say I prefer the way FrankT arranged the icons to how Darth did it. It now looks visually confusing whereas the score as a centerpiece (on the license plate) brought balance to the UI. My advice would be that the grille is more than big enough to support 5 icons, just have the current ones follow the bend of the fender and place the inventory above them in the middle. One variation you could try involves changing the inventory icon to an up arrow indicating that the inventory is 'under the hood':
and then make the inventory gui actually look like the top of the desoto engine with a bunch of stuff thrown about inside (dead weasel, etc)...
I went ahead and softened the shapes in the headlights rather than just reducing them in size as I thought they otherwise fit pretty well. I also doctored up the license plate a bit but you could make it plain if you want, my main recommendation would be keeping the points arranged in a license plate number fashion like I've done. I'd also recommend removing the black circles under the fender as they are really dark and distract your attention away from the rest of the gui and serve no real purpose. You can also safely reduce the size of the main icons without sacrificing clarity or usability, which will allow you to more easily fit your inventory icon (or an alternate one like in my example). I like the gui overall even if it is a bit large so I hope this helps!