Pretty neat, but I am sure there were no extra Sperry or Nordon available. They were guarded like gold and removed from the bomber between missions. All were super secret.
Yes, it's a Douglas A20 or DB-7 Havoc taking off, followed by a Bristol Blenheim flying over low (or possibly, if we are in Hollywood, it's Canadian-built equivalent the Bolingbroke) before it settles down into a Wellington.
Note also how huge the space the boffin is in is - bit like Con-Air, where the plane is ten times bigger inside than out!