You can order decals from Pattos, he will make them any size that you like. 1/43rd (O) scale decals would be much too big. "HO" cars are not actually HO scale, which is 1/87th. The cars vary in scale between 1/76th (OO scale) and 1/64th (S scale). If you want a perfect fit you will have to measure the body and have the decals sized to that.