Do you have the capability to make your own decals? In the old days windows, grills, vents and things like that would be provided in the old solid wood kits.I can't fdo it but maybe you can or know somebody, or somebody here who might be willing to do it for you. You will have to provide sizes and dimension for the curved areas.
Or, maybe get a black or silver decal sheet and cut your own. You may have to come uf with a way to slice the engine grill if its just a series of metal strips.