I'm no expert so take this for what it is worth. The following is to the best of my knowledge, based on what I have read and pictures I have seen. Most of this info comes from Northrop Flying Wings by Pape and Campbell.
All XB-35 (props), YB-49 (jet), and YRB-49 (recon) were flown in bare metal. Fifteen XB-35s were built or partially completed. One was converted to the sole YRB-49. Two YB-49s were built.
Northrop's XT-37 Turbodyne was never installed in any airframe but was planed for the EB-35B test bed, an XB-35 conversion that was never completed.
With the jet engine coming online, the fate of the XB-35 was uncertain. Would there be a contract for the B-35, would the completed/partially built airframes be converted to jets, or scraped? It seemed in 1948, no one knew what would happen, and the XB-35s were put in temporary outside storage. I believe the OP's photo is of work being done on a YB-49 while the XB-35s in the background were prepared for, or in, storage until their fate had been decided.
The XB-35s were initially to be converted to jet power but were scraped from 12/29/1949 to 2/4/1950. One of the XB-35s had became the EB-35B (the Turbodyne test bed). It, along with the YB-49 and YRB-49 were not ordered to be scraped with the XB-35s. However, the sole remaining YB-49 was destroyed in a taxi accident in 3/15/1950. The EB-35B was never completed and order scrapped, which it was on 3/30/1950. The YRB-49 continued flight testing until 1951. It was order scraped on 11/17/1953 and the deed was done by 12/1/1953.
Bill Pearce