Id suggest masking it with a decent, fine masking tape, and brush painting it. Other than that I'm pretty sure plain black lines are available for either aircraft use or model railways, but then it would be difficult getting the right width and length. I tried printing decals before, but you need a really good printer to do a decent job.
To update this, true to their word, Revell have provided another decal sheet. All that remains is to fit the door mirrors and the decals. The mirrors need drilled holes and I forgot before uniting the body and interior. A cheap mini drill should be here tomorrow.
The body moulding is quite rough and has a few sunken bits so a bit of p38 may be needed. On the finished ones I've seen, the stance is high at the front as per the rally cars and the rear wheels don't fill the arches. I plan to space out the wheels a bit a raise the rear just a touch. The moulding on the rear arches is very thick so I'm going to thin it slightly for clearance.