The Focke-Wulf 190 D-9 did have some variation of its armament during the development. The Technical description in February 1944 states that the D-9 could have the Motor Cannon MK 108 without the fuselage MG 131's as there was room for it before the fuselage front frame. Also, two MG 151's could replace the 131's (with no motor cannon).
However, these options seem to have been dropped, and the 213 C engine with the VS-9 propeller would also have been required to allow the shells to pass through, as the standard Jumo 213 A used in the D-9 had a reduction gear and VS-111 propeller that did not allow shells to pass through due to their design which blocked the shaft.
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