[olefebvre]

An E-7 did not necessarily have a DB601N installed actually the number of E-7/N and E-7/Z which were equipped with this engine was fairly low.
The saddle tanks were required not because of the DB601N but due to the introduction of the droptank, oil amount was insuficient using the standard oil tank given the extra 300l of fuel.
E-7/E-8 standards basically meant that, piping/wiring for the droptank and a few other changes (using the E/B as a basis). It should have had the DB601N as well but they gave so much troubles that the E-7 were built w/o except for the few E-7/N and E-7/Z.
The official designation for the type is E/B with modifications so as to carry a droptank, 4 MG-17s equipped a/c are to be know as E-8 and 2MG-17 and 2 MG-FFM a/c are to be known as E-7

So denes if your 109 could use a droptank it's an E-7...

btw Externally besides the octane triangle there is only one way to identify an DB601N equipped Emil...