I've believed it was due to the dimension of the radiator core and the proximity of the fan too it.Isn't it at it's very closest on the Novas? Possibly consider too,the Fan clutch has a longer attachment neck then the shorter fan spacer required on the Novas 5 bladed fan.
Cumby has an L-78?...does he know that?
I believe the early assembled solid lifter 1970 Chevelles-Novas came with the Hockey stick design,and the later built,(around late Dec. mid Jan 70),started to receive the shorter over valve cover design.And because the Hockey stick design,(No room for A/C equipped),was used mostly on the 1968-9 models,I always chalked it up to Chevrolet using up the old inventory on the early assembled 1970 solid lifter models first,then started using the later issued over valve cover design,(A/C acceptable),more rapidly on the later 1970 solids like Nova-Chevelle-new Camaro and ALL the detuned engines now requiring A.I.R. soon afterwards.
I've yet to see ANY 71-72 vehicle with the Hockey stick design.
I don't think the Dual snorkle design had anything to do with the A.I.R. tube design directly,just a coincedence that the Dual AC & over valve cover design were both in useage at the same time period,before that dual went the way of the Dodo.
I believe the Dual Snorkle air cleaner was originally intended for the 1970 LS-6 Corvette only.
When that didn't get the LS-6 nod for it's late 70 debut,Chevrolet began to use up that air cleaner as much as possible by mingleing it in with the Open Element air cleaner before cancelling it the following year.
Just my .03