We have had tremendous support from Karlheinz Rohrwild and other members of the Feldbahn Museum. See: www.feldbahn500.de.
With respect to locomotive No. 12691, Karlheinz sent us the following information:
From: Rohrwild, Karlheinz [mailto:
Sent: 29 June 2011 09:11
Subject: AW: Bloem.SANRASM O&K Locomotive
Here are the O&K plates over the years. Take a look at the second last in the middle row.

Have a nice day,
Karlheinz
----------
From: Rohrwild, Karlheinz [mailto:
Sent: 04 July 2011 09:43
Subject: Bloem.SANRASM O&K Locomotive.
Here I found another part in the puzzle. This is a drawing of a O&K boiler of a „Baulokomotive“ (Construction – Locomotive) with 50 HP from a 1939 magazine. I hope the measurements are equal to the boiler you are looking for.

In a couple of days I will get the picture I have send you with my last mail as an original. Then you will get it even better than now.
You have a good week,
Karlheinz Rohrwild
----------
From: Rohrwild, Karlheinz [mailto:
Sent: 10 August 2011 16:06
Subject: AW: Bloem.SANRASM O&K Locomotive.
There is something more I found in the net about the O&K locomotive.






I think now we got it all together.
Have a nice day,
Karlheinz
