For the curved corners on your cowl, it comes in handy to save sleeper roofs, and air spoilers etc for things like that. Ive scratchbuilt many cabs, and Ive been bailed out several times by using pieces like that. The top corners of a sleeper roof would have been perfect, but Ive done it with putty just like you did. Whenever I kitbash an Aero truck, I throw all of that stuff in a junkbox. Its been usefull in scratchbuilding more often than not. Great job, by the way. Im enjoying this build.