Is it possible to assign an arbitrary MAC address to an VirtualBox virtual machine instance? This answer suggests that it is only possible to generate MAC addresses where the most significant byte is a multiple of 2.
I have no idea where you got the idea that any part of a MAC address had to be a power of two from that answer... it only specifies that the first octet has to be even, which isn't a virtualbox limitation, it's an Ethernet one (if that bit is '1', it's a multicast address). The comments on that answer explain this. Feel free to try to assign such an address if you like, but don't expect anyone to do anything other than point and laugh when you tell them it doesn't work.