Well I dont fly in the MA anymore, But I use the Boston a lot in the CT and in the Histrical plane set's I do prety good with the 30cal's in Boston aganst Zero's and 109E's.
I beleave that the Ventral gun on the A20 is a 50 Cal, I may be mistaken though, it may be a 30cal, the TBM is a 30 cal in the ventral, but it is a diferent beast all together. Most of the guys who get me in the Boston/A20 do so from below the covered arc of the to position a ventral gun would realy help.