Development of the DB601A Engine mounted gun.

[schwarze-man]

I have found it difficult to get info about the development of the DB601 engine mounted gun, particularly for the Bf109E.
I have found details for the Bf109F and onwards, but the developments with the earlier 109E series and the prototype development seem obscure. I wonder if I am just missing a great reference on this subject?
My own attempts at research in the Bf109E Ersatzteil-liste do not show any reference to Engine mounted weapons, other than the top mounted guns.
The DB601A has the blast tube and mounting point for a hub firing gun, but no references to any gun or gun fittings for one. The closest thing I have found is the open spinner with blast reinforcement, that was fitted to some 109E aircraft. The 109E fuselage possibly has a cut-away at the front where the gun and its mount would probably need to fit but, the engine oil tank seems to occupy that space. Also, it would seem that the machine-gun ammunition boxes may also be an issue, certainly if the engine gun had a drum type ammunition feed.
I would be grateful for any info, or advice about this.
Cheers

SM