I am afraid that I don't have the time I thought I was going to have but can quickly deal with the comment Kurfurst made about the Pilots notes for the Spit II.
There are two sets of pilots notes for the Spit II both of the dated June 1940 which is confusing. Kurfursts one states both types of fuel mine only 100 octane so there is an obvious queston as to which one applies at what time.
The decider I believe is in the other details in the pilots notes. The one Kurfurst quotes in section 35 and the gun controls goes into detail about how to choose the 20mm and/or the LMG's. The one that I have only talks about one firing choice withthe 8 guns specifically mentioned in item 44.
As we know the Spit II in the BOB was only armed with 8 x LMG so I believe that this is the one for the BOB period.
Twin fuel options for the 20mm cannon armed Spit II does make sense in early/mid 41, as the Spit II was quickly followed into service by the Spit V and the earlier Spits transfered to training roles which used 87 Octane fuel.
I attach links to both sets of notes for people to look at and comment on.
The version Kurfurst has
http://www.plane-design.com/document...e%20Manual.pdf
The Version I am referring to
http://www.ww2aircraft.net/forum/oth...uals-9050.html
So to sum up I believe that the 8 guns version with only 100 octane fuel is the BOB version. The 20mm gunned version with both 87 and 100 octane fuel is post BOB when in training command.