Hmm. My players haven't gotten to Wyvern Tor, but this the the way I'm planning it out that's been mostly adapted from one post elsewhere that I can't remember anymore. Here are the notes I've made on it with one major approach that can branch off in a couple of different ways to deal with the orcs and a more straightforward approach:

They'll come across a single orc on water fetching duty who's pissed off at the others. A hand of Yurtrus has taken over the raiding party after their leader was killed, usurping the water fetching orc's claim to leadership as the second strongest orc in the band. The orc, in a compromised position (he doesn't want to spill the water and risk being torn apart by the other orcs), will surrender if the party lets him. If they ask him about the orcs, their numbers, etc. he'll generally help them out because he doesn't care if they live or die at this point. However, he'll also drop hints that he just wants to kill the leader, the hand of Yurtrus. If they follow this thread he'll tell them that if the hand dies the rest of the band will follow his lead and he'll assure them free passage and promise to leave the area (saying something about how there's not anything worth raiding around here anymore anyway) if he can be installed as leader of the band. If at any point during this plan the party says they won't go through with it the orc'll just go into the cave, tell them about the weird people outside, and bide him time for a later attempt to take leadership of the band.

I'm going to be using a modified version of the orc stronghold map in Volo's that's a lot smaller and doesn't have any of the gods' worshiper areas apart from Gruumsh. Some of the orcs will be out on patrol, others will be sleeping when the party comes in. The back entrance will still be there, but the orc won't think to mention it unless they ask about other ways into the cave; the water orc will not want to use it. They can find it themselves with a check if they say they want to investigate around the cave.

If the party goes in with the water orc they don't get to stealth in. The orc will just walk in and challenge the hand in a leadership contest. According to some orc tradition each of the claimants has a pack who fight with them. The water orc picks the party (there'll be some shouts about how weak it makes him look to use aliens as his pack), the hand of Yurtrus picks an equal amount of orcs to the party. All the other orcs will stay out of the fight. If the water orc dies in the fight the rest of the orcs will join in the attack on the party whenever that happens. If the hand of Yurtrus dies and the water orc is still alive the rest of the orcs stop fighting and accept him as their new band leader. At that point he'll renege on his word and call for them to attack the party. If over 3/4 of the total number of orcs in the cave system are dead every orc rolls a wisdom save. On a success they try to flee, saving themselves. On a fail they take the "aggressive" action on their next turn and continue attacking.

If the party ignores the water orc's plan, either killing him at any point or just ignoring him and either going around him or waiting till he gets back to the cave they can do whatever they want to take out the orcs instead of just charging in. The traps will be in place at both the main entrance and the side entrance, the secret entrance off to the side is still there, and most of the cave will be dim. The livestock pens are fairly loud which will obscure noise near them, and several orcs are mock-fighting in the main war chamber which is making a decent amount of noise. Orcs in this scenario will only flee if a) the hand of Yurtrus dies b) the party has gone loud and are enagged in open combat and c) they themselves are engaged in open combat with the party. They will make a will save to see if they actually flee or keep attacking when this happens. Otherwise the orcs will attack wherever they're alerted to the party and won't normally retreat.

I haven't come up with loot, but I think they deserve something more than the adventure says for getting through this. Maybe some objects worth a decent amount, but that are unwieldy or some things that seem orc specific and worthless, but have decent value.

Feel free to grab anything from my plan. I don't know how much is able to be applied, but there it is. If I hand to make a single suggestion I'd say molding the cave after the stronghold in Volo's is the number one thing to do. It really adds a lot of character to the encounter.