Jeff,
I "believe" the inside of the topper looks similar to the smaller, cone-shaped 70-series' topper, more or less.
I would also tend to think that there would be little difference in airflow through these toppers then.
Could one forgo the OEM topper and fit a Donaldson TopSpin? Anyone done this? Would someone be able to measure the diameter of their OEM snorkel tube?
http://www.colomboengines.com/donaldson/areatecnica/menu_air_file/F111107 TopSpin Pre-Cleaner.pdf