This is the place where the majority of the warbird (aircraft that have survived military service) discussions will take place. Specialized forums may be added in the new future
As you can imagine, there is no 'standard' when it comes to the rear jump seats added to P-51's, so there is quite a range in types of seats used and how they're mounted - usually with a means of quick-release and tilt option so that the area behind the rear seat can be accessed for storage and/or placement of modern avionics units (just as most (but not all) of the Mustangs that have rear seats fitted also have quick-release attachments at the top and mounts at the bottom of the front seat that allow it to tilt forward, providing more room for the passenger to enter the back seat).
This is a photo of the back seat fitted to Tom Duffy's P-51D "Kwitcherbitchin" (formerly "City of Winnipeg").
These are a selection of photos from Mike Vadeboncoeur/Midwest Aero, showing the rear seat installation on "Daddy's Girl" (which is also one of several stock P-51D airframes that has basic dual controls for the position in back). This one has a Warren McArthur style seat.
These are a few photos of the back seat on the P-51D "Miss Kandy" (formerly "Dixie Boy").
And this is a photo of the back seat of one of the Australian P-51D's, using a Schick Johnson seat. This one also has basic dual controls (note the stowed control stick and throttle - the rudder pedals for the back are fitted below the pilot's seat).
Following Mark's post, I don't recall where I found this photo, but it provides quite a unique view into one of the original two-place modified P-51B/C's (of which I believe there were as many as 10 modified in England during the war, and perhaps as many as 4-6 P-51D's with the split canopy/rear seat mod). In this case, the aircraft has dual Malcolm hoods. It has a Warren McArthur seat in the front and a Schick Johnson seat in the back (both seat types were used throughout P-51 production and could be interchanged). Note the position of the crank from the Malcolm hood kit for the rear unit, fitted via a bracket to the stock A-frame rollover support. The leather headrest is out of a P-51D/K.