Ah now, that's a new point entirely... Base eight or twelve? What's your thinking with that?
I'm guessing that your base eight idea is to be binary compatible (albeit that it's a 3-bit 'byte' (or whatever's one less than a nybble/whatever), which is a strange number that makes memory referencing a strange art, where 2^(2^n) would be a better choice[1], such that hexadecimal is probably the better choice.
Base twelve you're going for much as per the ancients who liked to easily divide by 2, 3, 4 (also 6), right? Admirable.
Of course, we're going into the realms of switching whole thinking-systems, whatever way. Not just a new scale, but a new order of magnitude. Of course, in computers we can do anything (base negative-pi, anyone?
), but that's something else.
Anyway... real physical properties? Best bet is, e.g. a mass that is a nice round number of hydrogen atoms (easily agreed by all races throughout the universe, taking isotope concentrations into account). Oh, but "nice round number" 1x10^?. Or some power of 2, 4, 8, 12, 16, 42, 60, 8128? Somewhere there's arbitrariness, and who knows what number of pseudopod-endings our galactic neighbours generally count on..!
[1] And ideally 'n' being itself a 2^? value, recursively, until you reach 2^1 (and thus 2^(2^0)).