Well, the attack of the balor is +33 with the long sword, let´s see +20 BAB, +1 weapon focus, +1 enhancemet boun and -1 because of the size. total +21, so the his str must be 35 (+12 bonus).
The damage them must be 2d6+13 +1 vorpal long sword, 1d4+7 +1d6 fire +1 flaming whip or 1d10+12 slams.