If you think that 206cm is way too small for a big guy then I think that 193cm is too tall to train him as a guard.
193cm is definitely too small for C-training but 206cm shouldn't be that bad. However, training a 206cm guy in handling or perimeter defense will be a pain
I relate more to the first one, that is 193, and he is too small for c/pf.The second is slightly better, but, like a said , can be better, if he want more pop-up in inside skills.
yes, to train a 206cm guy in handling or perimeter defense it will be difficult, but it's a good height for a SF, and it will be easy to train both skills, inside and outside.