Devere 203 max neg size with different heads

Hi, I am thinking about getting a 203. How come with the varicon head, you can en.arge ux9 negs but with ilford 400, 500 and dichromat heads it can on enlarge 6x7 negs. Any chance of getting the ilford heads or dichromat heat to cover 6x9, without raising the light source above the neg carrier