[Seaplanes]

I can contribute With the following Ju 52 engine test-beds:
Awailable for the Weser Flugzeugbau on 30. September 1940
W.Nr. 6388 DB601E centre engine
W.Nr. 5838 BMW 800 cenntre engine
W.Nr. 5708 Jumo 206A centre engine
W.Nr. 5581 DB 603 centre engine
W.Nr. 5035 DB 603 centre engine
All five Aircraft had normal BMW 132 wing-engines.

The Junkers Flugzeug und Motorenwerke had a total of six Ju 52/3m's allocated for the test of the Jumo 222 engine. Status on 30. September 1940 were: W.Nr. 1347 (V-205), W.Nr. 5353 (V-206), W.Nr. 5579 (V-207), W.Nr. 2975, W.Nr. 5299 (V-212) and W.Nr. 303.

Ju 52-aircraft used as engine test beds by Junkers Flugzeug und Motorenwerke by 30. September 1942:
W.Nr. 2975 (V-205) Delivered to Jumo for testing of Jumo 213.
W.Nr. 5353 (V-206) In Rechlin for testing of Jumo 213.
W.Nr. 3036 In Tarnewitz for testing of MG 131Z gun installation.
W.Nr. 7526 at JFM for testing of sandfilters.

Ju 52-aircraft allocated to Deutsche Lufthansa for engine testing by 30. September 1942:
W.Nr. 5828 DB623 as centre engine.
W.Nr. not known Jumo 207D as centre engine.
W.Nr. 6001 BMW 803 as centre engine.

Ju 52-aircraft allocated to Weser Flugzeugbau for engine testing by 30.September 1942:
W.Nr. 6388 DB603 as centre engine.

Hope this is of interest for someone.

My Source is Bundesarchiv-Militärarchiv Freiburg Akten RL3/906 and RL 3/1022