I made a mistake of drilling some additional holes that would eventually form the groove. The holes where all over the place and as I found out that the Dremel cutting disk didn't have any problems on cutting this stuff, the holes were totally unnecessary.
Two pieces cut, two more to go. I decided to keep the pieces together as long as possible as I don't have a wise here. This allowed me to keep the work piece better under control.
And now some threads. M6 bolt will be passing through here so first I drilled 5 mm hole and used M6x0.75 tap and after that M6x1.0 .
I was surprised how time consuming cutting aluminum can be. The hack saw that I used had a relatively new blade on it but still the process took a lot of time.