I have one regular and one heavy-duty "flying parts" or whatever
they are called hole cutters. The heavy duty is too big to cut a 40
mm hole. The small one probably won't cut 1/4"+ thick 6061 aluminum.
I'd rather try something like this...

https://www.amazon.com/gp/product/B0...3H6VU16E&psc=1

Can you tell what sort of shank it has? I doubt square will work.
Round might work. I would prefer hex.

Any suggestions for a 40 mm aluminum hole saw, to be stuck in a
drill press?

Thanks.