Wolfie, what references do you have to help you with the project? There is an excellent book on the B-32 that is invaluable (recommend search on Amazon to find it - Consolidated B-32 Dominator: The Ultimate Look, from Drawing Board to Scrapyard by William Wolf (Hardcover - Feb 2006) - Illustrated), being chock full of information re: the development and lots of engineering information.
The previously noted article by Gerald Asher would be a good source of inspiration. I saw his model at the IPMS/USA national convention in Dallas, TX a few year back, and it was most impressive. The description provided using B-29, B-24 & B-36 (1:72) kit parts is certainly workable, as this was how he did it. You can also create your own vacuform masters from wood, etc and make vac shell parts, but given the size of the components, it would require real effort to build a large enough vacuforming platen and practical tooling. Alternatively, you can use the masters to create fiberglass parts using the materials from the "RC aisle" of the hobby shop. These would result in parts that are light, hollow and rigid, plus you'd learn some valuable techniques. 'Glass mold making is a great way to get into using the resins for modeling.
Also occurs to me that you can make the components from ESP foam, aka "blue" foam. And of course, the previously recommended plank on from is a time-honored method. I've seen a 1:48 B-17 constructed this way (pre-Monogram kit days...) where half-frames were mounted on a board just like building a balsa model, and then planked with plastic strips.
I suppose you are only limited by your imagination re: the scratchbuilding method and of course how much time you wish to devote to the project. Don't want to "run out of steam" after all!
Good luck with it!
Regards, Robert