The only cab that is 7 feet (bbc)is the vans like the Ford E-450 used in the smaller Class C motorhomes.

The usual MDT cabs are about 8 1/2 feet BBC. (bumper to back of cab). The Freightliner M2 is in that size in the 106 model. When you move up to the class 8 cabs, like the Freightliner Columbia they are at least 10 feet. Some of the long hood models like Peterbilts and Kenworths can be 11 to 12 feet.