The really nice thing of the Aspect Ratio method is that it works equally weel with yards or metres, feet or decimetres....

So I would suggest that you modify the manual to actually replace the mast height (Unless it breaks the stadimeter) with the aspect ratio. So you can have the aspect ratio directly for AOB, and the length for the speed measurement. If that fails, could the AR be added behind the lentgh in the same line? F.e. in the Mogami example, you would read something like this:
Length = 656 ft (AR 5.77)