not in the slightest, very possible
sor won't even come close to being in contention for top 10 units
so that leaves:
Math ext.2) 1/8
Math ext.1) 4/34
English Adv) 8/26
Chemistry) 1/36
Phyics) 1/48
boy in my grade did the exact same subjects [school rank 160~]
except physics was ranked one lower, english he was ranked 2 lower albeit in a class of 40, everything else very similar.
got 99.6
missed out on med and to rub salt into the wounds missed out comm/law his 2nd choice by 0.05 lol
you'd be surprised i think!
just to reinforce further:
2010 hsc - my ranks
1/11 - legal studies
3/60 - maths 2u
4/20 - maths ext 1
4/40 - english adv
4/100 - sor 1u
5/40 - economics
nowhere near the scaling of his subjects and i still pulled off 98+
so i'd be surprised if his ranks and subjects didnt equate to 99+