Type of gear oil or transmission fluid for Farymann K34?

Hi everyone,

Getting ready to try starting up a Farymann in our Contessa, which has been out of the water for 5 years.

Engine is in surprisingly great shape.  Cranks fine by hand with decent compression. I have a replacement impeller in hand. We have drained the old diesel and engine oil.  Also, we removed the transmission fluid for good measure.  Now looking to replace the tranny fluid, and cannot find any information about what to use.  My research (and a hand written note in a shop manual kindly sent by Ian) suggests ATF, while my engineer friend insists that this must be gear oil of some sort.

I purchased a quart of Mobil 1 Synthetic ATF, rationalizing that it probably would work fine.  Any wisdom out there?

Thanks!