I'm not sure I'd bother bringing regular Orc Boyz. Goblin units aren't good, either, to be fair, but they provide the static combat score you're after for a lot fewer points. They can (usually) hold an opponent in place for a turn for your Black Orcs to charge.
Alternatively, if you don't mind the infuriating fact that Games Workshop doesn't produce plastic models for them, you could bring large units of Savage Orcs, which are... savage. Frenzy is, in my experience, the most underestimated ability in the game because everyone assumes you'll just find a way to draw them off. The reality ends up being pretty different, as you have to go out of your way to do that, and have to have the right unit to do it with. Most armies don't have the wiggle room to mess with drawing out a Frenzied unit like that, and even if they do, they have to do it in such a way that the Frenzied unit can't see any other target to potentially charge (even if it's a failed charge.) Long story short, Savage Orcs are excellent, and far better than regular Orc Boyz.
Ultimately, you'll need some goblins. It's a sad fact of life when you're a greenskin, it seems. One of the things that makes it possible for Orc units to win fights is decent shooting, and that's provided almost entirely by goblin units such as Spear Chukkas, fanatics (which isn't really shooting, but it's got a similar role and is resolved in the same way), and outrageously maneuverable fast cavalry such as Spider and Wolf Riders.
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