Some further thoughts
To pick up on a few comments. Around 500 Me109G-12s (the 2 seat version) were built from 1944 all converted from existing G series airframes. They were in response to the loss of trainee pilots especially in take off and landing accidents. The second seat took up most of the original fuel tank so they were very short ranged and used for take off and landing instruction.Few retained armaments.
Bf / Me 109s did not have a successful engine mounted cannon installation until the "F" model - post Battle of Britain. The two guns firing through the prop had a reduced rate of fire due to interruptor gear. Possibly resulting in retaining 3 blade props even with the more powerful DB605. Original 109s had two blade props.
I'm not sure if the one offered for sale is airworthy. There is one other "G12" flying being a conversion of a single seat Buchon in 2013. That one has interchangeable RR Merlin 500 and DB DB605 engines. Most of the flying is likely to be carried out with the Merlin being a lot less rare than the DB605.
The inverted V engine is possibly easier to service as most of the valves etc can be reached by someone standng on the ground whereas Merlin installations required ladders and / or platforms. RR did consider an inverted V for the Merlin but legend has it that such a configuration was considered too Germanic....
BoB film used a B25 Mitchell as a camera platform rather than B17.
As well as Standford Tuck, other RAF pilots contributed including Ginger Lacey and Douglas Bader.