I've cut through some thinner aluminium with a cheap hole saw. Took a while but worked fine and the saw managed OK. I think I did 3 pieces of 4mm thick sheet which is 1/2" total. That was only a 20 mm hole saw though. The other problem would be accuracy, you probably won't find a 56 mm hole saw and if you do it will probably cut 59 mm holes...

I guess ideally you would want to use a milling machine and a boring bar to cut a hole that size, if you can get access to one.