Assuming all the animals are acting according to their normal nature, the only way this fight would even occur would be for the lion to be outrageously hungry and desperate enough to go after one of the gorillas.
The lion dosent have to be desperate, he takles animals that dwarf the world record silver backs... size, ferocity, power, agression and ability to kill by 2-10x fold...
http://teamauthority.myfastforum.org/ftopic623-0-asc-30.php
The Gorilla is weaker, slower, less-agressive and smaller than all of those animals, it would literaly be a mismatch if it was one on one.
If the lion attacked from ambush or ran down its target, it would have to succeed in first getting a throat hold on the gorilla, and then be able to hold out against the bashing the gorilla would be giving it for a good 1-2 minutes while it attempts to suffocate the prey. I'm not sure a lion could put up with that amount of abuse, so I'd give the fight to the gorilla, who will do enough damage to the lion to either escape or possibly even kill it.
Ambush? How, he lives in the open savanah mostly now, his days of the King of the Jungles of India is almost up. The lion is known by many sources (which I have on hand) as a fighter, not a hunter; he dosent just ambush and assasinates like the rest of the cat family, he chooses to to take head on his opponents.
The lion is alot more durable then the gorilla, since he has 20 razor sharp claws that can all be out into play, and if any of them make any contact toppled with a force that can break a zebras neck with a well placed blow would be devistating to a gorilla, bleeding to death is a major factor to exaustion; which the lion is the athlete here, not the clumsy gorilla.
You've actually never seen a lion in action (fighting) have you, let me tell you; its a thing of beauty, cant say the same about silver backs fighting...other than fictional King kong movies, lol...A lion would overwhelm a gorilla too much, leopards as I linked a few pages back, can do the job, the lion is the big cats most superior fighter next to the tigers supremes hunting skills, I would never favor a gorilla when they get decimated all day by 120 pound cats, thats being respctively honest and not down grading since all the animals that showed game to lions are rare events; on average stuff like badgers who some times scare the occaisonal curious juvi would get eatin by a smaller cub who has the will to oppose.
Now, if instead we assume all these animals have all been to MMA camp and are extremely aggressive (not to mention smarter than the average bear) then the lion has zero chance. The gorillas will run him down, surround him and take turns pummeling him as they run by, never once grappling with the lion to give him a chance to use his claws, rake or bite attack.
Wait...did someone say something about beer?
Man is incredibly smarter than any gorilla; ever, yet hand to hand a man would be a screaming mess against even a 2 year old lion if he choses to kill you. Tigers, lions and leopards clear out villages of hundreds when they are on the attack, you'd think people would say, ahh, we are 100's he is just one...attack!...But its more like, RUN!
lol