I found this just now, and it was a very interesting site from both a modeling and historical perspective. It notes all of the components of the B-29 that were supplied by various auto manufacturers. There are some very nice period photos and a list of the serials of all the Martin-built B-29's, including two of the more famous Silverplate aircraft. The Martin-built Superforts were said to be the highest quality, and when Col. Paul Tibbets toured the plant to see how production of the Silverplate Superforts was going, he personally selected the one that he was going to fly. I thought this might be of interest.
Mike
https://usautoindustryworldwartwo.com/b-29-usautoindustry.htm