I am currently trying to modify Revell's viic into U-99

I have scoured the internet and have several German books with construction drawings BUT I just can't figure out U-99's sail configuration.

U-99 was a type viib and I have read ( and in fact my blueprints bear this out) that type viib's had the ugly external air intakes on the tower as compared to the more hidden ones inside the tower of viic's.

So I started building these ducts but then found several pictures purporting to be U-99 ( at least two of which came from someone who knew and extensivly interviewed Otto Kretschmer) and they do not show this feature. The boats in the pictures all have the horseshoe on the tower but there were of course others using this symbol.

Does anyone know for sure (yeah I kmow it's not possible) if U-99 had the external ductwork or some other configuration?

Thank you in advance

Thomas