I was in the exact same situation as your husband. I converted my EASA license to an FAA one. After the written test I was also considering the options for the checkride. I decided to do a shortened type rating course for the aircraft I had flown for almost 20 years. The advantages are that there are no surprises in the actual checkride and the the oral part is a piece of cake. The Examiner admitted that I knew more about the aircraft than him. From what I’ve heard the oral in a light piston aircraft puts way more emphasis on the general ATP stuff. And who wants to get grilled over Aerodynamics or Meteorology or whatever subject you don’t like? So in the end I’m very happy that I paid a bit more and didn’t have to worry about anything. Needless to say that a jet type might give you an advantage for a possible application to the airlines. Good luck with whatever route your husband is going to take.