This requirement doesn't make sense to me. There is a truly impressive selection of tires available in 26 x 1.5; and the same goes for rims (including, for example Salsa Delgados). Do you expect to get some advantage from 700c that 26" won't give you?

Cold setting a frame from 126 to 135 shouldn't be a problem, since you're talking about a steel frame anyway. Don't do it with aluminum or carbon fiber, of course. Dropout alignment may be indicated; but again, shouldn't be a problem. Having a professional do it should be way cheaper than having Bilenky build the whole frame for you.