I have held a ruler around the 'edges' of each of the firetrucks. You can fussy cut one engine at a time and you will have a wide 'square'. Because one pattern of fire engine is not free enough to cut around and use each engine, measure about 1/2 inch around the intended engine and cut out to make a block of an elongated size. You will have sacrificed the engine beside/over/under this block, but can reverse the choice of cutting from the next. Then I would piece using navy or royal blue .... something to add to it's colour in a strip between each row. Another thought, the blocks will not be regimented so you could 'frame' each engine in say blue and use them scattered rather than in on straight line down.