I don't have it in front of me, but one of my B-36 books (I don't remember which) has a section on modeling. If I recall correctly, someone did a conversion of the 1/72 B-36 to a YB-60, although I don't know if a B-52 kit was used. There were pictures of the completed model, which was very impressive.
Sorry that this is so vague, but if you like I can dig up the book when I get home and post more information about it.
Mark