Don't want to roll HD for enemies? There is a simple way to handle HD. Usually in monster statistics there is average of hit points for HD marked. Or you can simply calculate it.
Without rolling HD you can easily assign them.
25% of maximum hit points for weak enemies
50% of maximum for normal enemies
75% of maximum to strong enemies
100% of maximum for bosses and really powerful enemies.
Weakling orcs (1HD) would have 2 hp, when normal orcs have 4. Seasoned warrior orcs would have 6 hp and orc chief would have 8.
Simple and fast.