Help with GRP Rear Framework

[baz-r]

bin d13 and tie in to your roll bar back stays or tubes then you can fit a good size tank as the tin back didnt have the strength the grp frame had.
i can stand on my unbraced grp frame and jump up and down and i must be 75-80kgs
25l tank is just too small

what i need is the side dimention to get my tank design right as i have no grp yet (gap from bottom of grp tub to diff box and top of diff box to grp tub both level mesurements)