Shouldn't matter.
The Air 740 already comes with 2x140mm fans preinstalled in the front, and there's clearly a gap between them right where a single GPU will protrude. If anything, that gives you MORE room for GPU length than having the front full of 3x120mm fans.
Corsair's website says "max GPU length = 330mm"
Asus' website for the Strix RTX2070 says "length = 305mm"
The top and bottom fan mounts aren't anywhere near a GPU.
How many RTX20?? cards are you planning on using? The stock fan setup should be plenty for most single GPU systems.