It should work--I looked at the dimensioning of my 5x7 2D with exactly the same thoughts in mind; 5x7 is such a nice format for portraits. The 375 Caltar is actually not all that big and heavy, as lenses go, and the weight will be fairly close to the front standard (which reduces the tendency to pull the standard out of line). However, a 14-3/4" lens is a bit on the longish side for 5x7, and the 12" Commercial Ektar mentioned by Barry S would indeed be a fine alternative.
I guess that I'd have to disagree, mildly, about the relationship between the lensboard size and appropriateness of lenses---I also have an 11x14 2D, and it's lensboard is almost the same size as the one for the 5x7!